[DEV] add v1.66.0

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2018-01-12 21:47:58 +01:00
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[section boost/python/args.hpp]
[section Introduction]
Supplies a family of overloaded functions for specifying argument keywords for wrapped C++ functions.
[section keyword-expressions]
A keyword-expression results in an object which holds a sequence of [link ntbs]\ es, and whose type encodes the number of keywords specified. The keyword-expression may contain default values for some or all of the keywords it holds
[endsect]
[endsect]
[section Class `arg`]
The objects of class arg are keyword-expressions holding one keyword ( size one )
``
namespace boost { namespace python
{
struct arg
{
template <class T>
arg &operator = (T const &value);
explicit arg (char const *name){elements[0].name = name;}
};
}}
``
[endsect]
[section Class `arg` constructor]
``arg(char const* name);``
[variablelist
[[Requires][The argument must be a [link ntbs].]]
[[Effects][Constructs an arg object holding a keyword with name name.]]
]
[endsect]
[section Class `arg` operator=]
``template <class T> arg &operator = (T const &value);``
[variablelist
[[Requires][The argument must convertible to python.]]
[[Effects][Assigns default value for the keyword.]]
[[Returns][Reference to `this`.]]
]
[endsect]
[section Keyword-expression operator,]
``
keyword-expression operator , (keyword-expression, const arg &kw) const
keyword-expression operator , (keyword-expression, const char *name) const;
``
[variablelist
[[Requires][The argument name must be a [link ntbs].]]
[[Effects][Extends the keyword-expression argument with one more keyword.]]
[[Returns][The extended keyword-expression.]]
]
[endsect]
[section Example]
``
#include <boost/python/def.hpp>
using namespace boost::python;
int f(double x, double y, double z=0.0, double w=1.0);
BOOST_PYTHON_MODULE(xxx)
{
def("f", f, (arg("x"), "y", arg("z")=0.0, arg("w")=1.0));
}
``
[endsect]
[endsect]

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[section boost/python/call.hpp]
[section Introduction]
<boost/python/call.hpp> defines the call family of overloaded function templates, used to invoke Python callable objects from C++.
[endsect]
[section Function `call`]
``
template <class R, class A1, class A2, ... class An>
R call(PyObject* callable, A1 const&, A2 const&, ... An const&)
``
[variablelist
[[Requires][R is a pointer type, reference type, or a complete type with an accessible copy constructor]]
[[Effects][Invokes callable(a1, a2, ...an) in Python, where a1...an are the arguments to call(), converted to Python objects. ]]
[[Returns][The result of the Python call, converted to the C++ type R.]]
[[Rationale][For a complete semantic description and rationale, see this page. ]]
]
[endsect]
[section Example]
The following C++ function applies a Python callable object to its two arguments and returns the result. If a Python exception is raised or the result can't be converted to a double, an exception is thrown.
``
double apply2(PyObject* func, double x, double y)
{
return boost::python::call<double>(func, x, y);
}
``
[endsect]
[endsect]

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[section boost/python/call_method.hpp]
[section Introduction]
<boost/python/call_method.hpp> defines the call_method family of overloaded function templates, used to invoke callable attributes of Python objects from C++.
[endsect]
[section Function `call_method`]
``
template <class R, class A1, class A2, ... class An>
R call_method(PyObject* self, char const* method, A1 const&, A2 const&, ... An const&)
``
[variablelist
[[Requires][`R` is a pointer type, reference type, or a complete type with an accessible copy constructor]]
[[Effects][Invokes `self.method(a1, a2, ...an)` in Python, where `a1...an` are the arguments to `call_method()`, converted to Python objects. For a complete semantic description, see this page.]]
[[Returns][The result of the Python call, converted to the C++ type `R`.]]
[[Rationale][`call_method` is critical to implementing C++ virtual functions which are overridable in Python, as shown by the example below.]]
]
[endsect]
[section Example]
The following C++ illustrates the use of `call_method` in wrapping a class with a virtual function that can be overridden in Python:
C++ Module Definition
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/utility.hpp>
#include <cstring>
// class to be wrapped
class Base
{
public:
virtual char const* class_name() const { return "Base"; }
virtual ~Base();
};
bool is_base(Base* b)
{
return !std::strcmp(b->class_name(), "Base");
}
// Wrapper code begins here
using namespace boost::python;
// Callback class
class Base_callback : public Base
{
public:
Base_callback(PyObject* self) : m_self(self) {}
char const* class_name() const { return call_method<char const*>(m_self, "class_name"); }
char const* Base_name() const { return Base::class_name(); }
private:
PyObject* const m_self;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
def("is_base", is_base);
class_<Base,Base_callback, noncopyable>("Base")
.def("class_name", &Base_callback::Base_name)
;
}
``
Python code:
``
>>> from my_module import *
>>> class Derived(Base):
... def __init__(self):
... Base.__init__(self)
... def class_name(self):
... return self.__class__.__name__
...
>>> is_base(Base()) # calls the class_name() method from C++
1
>>> is_base(Derived())
0
``
[endsect]
[endsect]

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[section Calling Python Functions and Methods]
[section Introduction]
The simplest way to call a Python function from C++, given an [link object_wrappers.boost_python_object_hpp.class_object `object`] instance f holding the function, is simply to invoke its function call operator.
``f("tea", 4, 2) // In Python: f('tea', 4, 2)``
And of course, a method of an [link object_wrappers.boost_python_object_hpp.class_object `object`] instance `x` can be invoked by using the function-call operator of the corresponding attribute:
``x.attr("tea")(4, 2); // In Python: x.tea(4, 2)``
If you don't have an [link object_wrappers.boost_python_object_hpp.class_object `object`] instance, `Boost.Python` provides two families of function templates, [link function_invocation_and_creation.boost_python_call_hpp.function_call `call`] and [link function_invocation_and_creation.boost_python_call_method_hpp.function_call_method `call_method`], for invoking Python functions and methods respectively on `PyObject*`\ s. The interface for calling a Python function object (or any Python callable object) looks like:
``call<ResultType>(callable_object, a1, a2... aN);``
Calling a method of a Python object is similarly easy:
``call_method<ResultType>(self_object, "method-name", a1, a2... aN);``
This comparitively low-level interface is the one you'll use when implementing C++ virtual functions that can be overridden in Python.
[endsect]
[section Argument Handling]
Arguments are converted to Python according to their type. By default, the arguments `a1...aN` are copied into new Python objects, but this behavior can be overridden by the use of [link function_invocation_and_creation.boost_python_ptr_hpp.functions `ptr()`] and `ref()`:
``
class X : boost::noncopyable
{
...
};
void apply(PyObject* callable, X& x)
{
// Invoke callable, passing a Python object which holds a reference to x
boost::python::call<void>(callable, boost::ref(x));
}
``
In the table below, x denotes the actual argument object and cv denotes an optional cv-qualification: "const", "volatile", or "const volatile".
[table
[[Argument Type][Behavior]]
[[`T cv &`
`T cv`][The Python argument is created by the same means used for the return value of a wrapped C++ function returning T. When T is a class type, that normally means *x is copy-constructed into the new Python object.]]
[[T*][If x == 0, the Python argument will be None. Otherwise, the Python argument is created by the same means used for the return value of a wrapped C++ function returning T. When T is a class type, that normally means *x is copy-constructed into the new Python object.]]
[[boost::reference_wrapper<T>][The Python argument contains a pointer to, rather than a copy of, x.get(). Note: failure to ensure that no Python code holds a reference to the resulting object beyond the lifetime of *x.get() may result in a crash!]]
[[pointer_wrapper<T>][If x.get() == 0, the Python argument will be None. Otherwise, the Python argument contains a pointer to, rather than a copy of, *x.get(). Note: failure to ensure that no Python code holds a reference to the resulting object beyond the lifetime of *x.get() may result in a crash!]]
]
[endsect]
[section Result Handling]
In general, `call<ResultType>()` and call_method<ResultType>() return ResultType by exploiting all lvalue and rvalue from_python converters registered for ResultType and returning a copy of the result. However, when ResultType is a pointer or reference type, Boost.Python searches only for lvalue converters. To prevent dangling pointers and references, an exception will be thrown if the Python result object has only a single reference count.
[endsect]
[section Rationale]
In general, to get Python arguments corresponding to a1...aN, a new Python object must be created for each one; should the C++ object be copied into that Python object, or should the Python object simply hold a reference/pointer to the C++ object? In general, the latter approach is unsafe, since the called function may store a reference to the Python object somewhere. If the Python object is used after the C++ object is destroyed, we'll crash Python.
In keeping with the philosophy that users on the Python side shouldn't have to worry about crashing the interpreter, the default behavior is to copy the C++ object, and to allow a non-copying behavior only if the user writes boost::ref(a1) instead of a1 directly. At least this way, the user doesn't get dangerous behavior "by accident". It's also worth noting that the non-copying ("by-reference") behavior is in general only available for class types, and will fail at runtime with a Python exception if used otherwise[1].
However, pointer types present a problem: one approach is to refuse to compile if any aN has pointer type: after all, a user can always pass *aN to pass "by-value" or ref(*aN) to indicate a pass-by-reference behavior. However, this creates a problem for the expected null pointer to None conversion: it's illegal to dereference a null pointer value.
The compromise I've settled on is this:
# The default behavior is pass-by-value. If you pass a non-null pointer, the pointee is copied into a new Python object; otherwise the corresponding Python argument will be None.
# if you want by-reference behavior, use ptr(aN) if aN is a pointer and ref(aN) otherwise. If a null pointer is passed to ptr(aN), the corresponding Python argument will be None.
As for results, we have a similar problem: if ResultType is allowed to be a pointer or reference type, the lifetime of the object it refers to is probably being managed by a Python object. When that Python object is destroyed, our pointer dangles. The problem is particularly bad when the ResultType is char const* - the corresponding Python String object is typically uniquely-referenced, meaning that the pointer dangles as soon as call<char const*>(...) returns.
The old Boost.Python v1 deals with this issue by refusing to compile any uses of call<char const*>(), but this goes both too far and not far enough. It goes too far because there are cases where the owning Python string object survives beyond the call (just for instance, when it's the name of a Python class), and it goes not far enough because we might just as well have the same problem with a returned pointer or reference of any other type.
In Boost.Python this is dealt with by:
# lifting the compile-time restriction on `char const *` callback returns
# detecting the case when the reference count on the result Python object is 1 and throwing an
exception inside of `call<U>(...)` when `U` is a pointer or reference type.
This should be acceptably safe because users have to explicitly specify a pointer/reference for `U` in `call<U>`, and they will be protected against dangles at runtime, at least long enough to get out of the `call<U>(...)` invocation.
[endsect]
[endsect]

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[section boost/python/class.hpp]
[section Introduction]
`<boost/python/class.hpp>` defines the interface through which users expose their C++ classes to Python. It declares the `class_` class template, which is parameterized on the class type being exposed. It also exposes the `init`, `optional` and `bases` utility class templates, which are used in conjunction with `class_`.
`<boost/python/class_fwd.hpp>` contains a forward declaration of the `class_` class template.
[endsect]
[section Class template `class_<T, Bases, HeldType, NonCopyable>`]
Creates a Python class associated with the C++ type passed as its first parameter. Although it has four template parameters, only the first one is required. The three optional arguments can actually be supplied *in any order*\ ; Boost.Python determines the role of the argument from its type.
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[`T`][A class type.][The class being wrapped][]]
[[Bases]
[A specialization of [link high_level_components.boost_python_class_hpp.class_template_bases_t1_t2_tn bases<...>] which specifies previously-exposed C++ base classes of `T`.]
[Registers `from_python` conversions from wrapped `T` instances to each of its exposed direct and indirect bases. For each polymorphic base `B`, registers conversions from indirectly-held wrapped `B` instances to `T`.][[link high_level_components.boost_python_class_hpp.class_template_bases_t1_t2_tn bases<>]]]
[[HeldType][Must be `T`, a class derived from `T`, or a [link concepts.dereferenceable.concept_requirements Dereferenceable] type for which `pointee<HeldType>::type` is `T` or a class derived from `T`.][Specifies the type that is actually embedded in a Python object wrapping a `T` instance when `T`\ 's constructor is called or when a `T` or `T*` is converted to Python without the use of [link function_invocation_and_creation.boost_python_ptr_hpp.functions ptr], `ref`, or [link concepts.callpolicies Call Policies] such as [link function_invocation_and_creation.models_of_callpolicies.boost_python_return_internal_ref.class_template_return_internal_r return_internal_reference]. More details below.][`T`]]
[[NonCopyable][If supplied, must be `boost::noncopyable`.][Suppresses automatic registration of `to_python` conversions which copy `T` instances. Required when `T` has no publicly-accessible copy constructor.][An unspecified type other than boost::noncopyable.]]
]
[section HeldType Semantics]
# If HeldType is derived from `T`, its exposed constructor(s) must accept an initial `PyObject*` argument which refers back to the Python object that contains the HeldType instance, as shown in this example. This argument is not included in the [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] passed to [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu def(init_expr)], below, nor is it passed explicitly by users when Python instances of `T` are created. This idiom allows C++ virtual functions which will be overridden in Python to access the Python object so the Python method can be invoked. Boost.Python automatically registers additional converters which allow wrapped instances of `T` to be passed to wrapped C++ functions expecting HeldType arguments.
# Because Boost.Python will always allow wrapped instances of `T` to be passed in place of HeldType arguments, specifying a smart pointer for HeldType allows users to pass Python `T` instances where a smart pointer-to-T is expected. Smart pointers such as `std::auto_ptr<>` or `boost::shared_ptr<>` which contain a nested type `element_type` designating the referent type are automatically supported; additional smart pointer types can be supported by specializing `pointee<HeldType>`.
# As in case 1 above, when HeldType is a smart pointer to a class derived from `T`, the initial `PyObject*` argument must be supplied by all of HeldType's exposed constructors.
# Except in cases 1 and 3, users may optionally specify that T itself gets initialized with a similar initial `PyObject*` argument by specializing [link utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc has_back_reference<T>].
[endsect]
[section Class template `class_` synopsis]
``
namespace boost { namespace python
{
template <class T
, class Bases = bases<>
, class HeldType = T
, class NonCopyable = unspecified
>
class class_ : public object
{
// Constructors with default __init__
class_(char const* name);
class_(char const* name, char const* docstring);
// Constructors, specifying non-default __init__
template <class Init>
class_(char const* name, Init);
template <class Init>
class_(char const* name, char const* docstring, Init);
// Exposing additional __init__ functions
template <class Init>
class_& def(Init);
// defining methods
template <class F>
class_& def(char const* name, F f);
template <class Fn, class A1>
class_& def(char const* name, Fn fn, A1 const&);
template <class Fn, class A1, class A2>
class_& def(char const* name, Fn fn, A1 const&, A2 const&);
template <class Fn, class A1, class A2, class A3>
class_& def(char const* name, Fn fn, A1 const&, A2 const&, A3 const&);
// declaring method as static
class_& staticmethod(char const* name);
// exposing operators
template <unspecified>
class_& def(detail::operator_<unspecified>);
// Raw attribute modification
template <class U>
class_& setattr(char const* name, U const&);
// exposing data members
template <class D>
class_& def_readonly(char const* name, D T::*pm);
template <class D>
class_& def_readwrite(char const* name, D T::*pm);
// exposing static data members
template <class D>
class_& def_readonly(char const* name, D const& d);
template <class D>
class_& def_readwrite(char const* name, D& d);
// property creation
template <class Get>
void add_property(char const* name, Get const& fget, char const* doc=0);
template <class Get, class Set>
void add_property(
char const* name, Get const& fget, Set const& fset, char const* doc=0);
template <class Get>
void add_static_property(char const* name, Get const& fget);
template <class Get, class Set>
void add_static_property(char const* name, Get const& fget, Set const& fset);
// pickle support
template <typename PickleSuite>
self& def_pickle(PickleSuite const&);
self& enable_pickling();
};
}}
``
[endsect]
[section Class template `class_` constructors]
``
class_(char const* name);
class_(char const* name, char const* docstring);
template <class Init>
class_(char const* name, Init init_spec);
template <class Init>
class_(char const* name, char const* docstring, Init init_spec);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules]. If docstring is supplied, it must be an [link ntbs]. If `init_spec` is supplied, it must be either the special enumeration constant `no_init` or an [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] compatible with `T`.]]
[[Effects][Constructs a `class_` object holding a Boost.Python extension class named name. The named attribute of the [link high_level_components.boost_python_scope_hpp.introduction current scope] is bound to the new extension class.
* If supplied, the value of docstring is bound to the `__doc__` attribute of the extension class.
* If `init_spec` is `no_init`, a special `__init__` function is generated which always raises a Python exception. Otherwise, `this->def(init_spec)` is called.
* If `init_spec` is not supplied, `this->def(init<>())` is called.]]
[[Rationale][Allowing the user to specify constructor arguments in the `class_<>` constructor helps her to avoid the common run-time errors which result from invoking wrapped member functions without having exposed an `__init__` function which creates the requisite `T` instance. Types which are not default-constructible will cause a compile-time error unless `Init` is supplied. The user must always supply name as there is currently no portable method to derive the text of the class name from its type.]]
]
[endsect]
[section Class template `class_` modifier functions]
``
template <class Init>
class_& def(Init init_expr);
``
[variablelist
[[Requires][`init_expr` is the result of an [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] compatible with `T`.]]
[[Effects][For each [link high_level_components.boost_python_init_hpp.introduction.init_expressions valid prefix] `P` of `Init`, adds an `__init__(...)` function overload to the extension class accepting P as arguments. Each overload generated constructs an object of HeldType according to the semantics described above, using a copy of init_expr's call policies. If the longest [link high_level_components.boost_python_init_hpp.introduction.init_expressions valid prefix] of Init contains N types and init_expr holds M keywords, an initial sequence of the keywords are used for all but the first N - M arguments of each overload.]]
[[Returns][`*this`]]
[[Rationale][Allows users to easily expose a class' constructor to Python.]]
]
``
template <class F>
class_& def(char const* name, Fn fn);
template <class Fn, class A1>
class_& def(char const* name, Fn fn, A1 const& a1);
template <class Fn, class A1, class A2>
class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2);
template <class Fn, class A1, class A2, class A3>
class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2, A3 const& a3);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].
* If a1 is the result of an [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions overload-dispatch-expression], only the second form is allowed and fn must be a pointer to function or pointer to member function whose [link arity] is the same as A1's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions maximum arity].
[*Effects:] For each prefix `P` of `Fn`\ 's sequence of argument types, beginning with the one whose length is `A1`\ 's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions minimum arity], adds a `name(...)` method overload to the extension class. Each overload generated invokes a1's call-expression with `P`, using a copy of a1's call policies. If the longest valid prefix of `A1` contains `N` types and a1 holds `M` keywords, an initial sequence of the keywords are used for all but the first `N - M` arguments of each overload.
* Otherwise, a single method overload is built around fn, which must not be null:
* If fn is a function pointer, its first argument must be of the form U, U cv&, U cv*, or U cv* const&, where T* is convertible to U*, and a1-a3, if supplied, may be selected in any order from the table below.
* Otherwise, if fn is a member function pointer, its target must be T or one of its public base classes, and a1-a3, if supplied, may be selected in any order from the table below.
* Otherwise, Fn must be [derived from] [link object_wrappers.boost_python_object_hpp.class_object object], and a1-a2, if supplied, may be selcted in any order from the first two rows of the table below. To be useful, fn should be [@http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6 callable].
[table
[[Mnemonic Name][Requirements/Type properties][Effects]]
[[docstring][Any [link ntbs]][Value will be bound to the __doc__ attribute of the resulting method overload. If an earlier overload supplied a docstring, two newline characters and the new docstring are appended to it.]]
[[policies][A model of [link concepts.callpolicies CallPolicies]][A copy will be used as the call policies of the resulting method overload.]]
[[keywords][The result of a [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] specifying no more arguments than the [link arity] of fn.][A copy will be used as the call policies of the resulting method overload.]]
]
]]
[[Returns][`*this`]]
]
``class_& staticmethod(char const* name);``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules], and corresponds to a method whose overloads have all been defined.]]
[[Effects][Replaces the existing named attribute `x` with the result of invoking `staticmethod(x)` in Python. Specifies that the corresponding method is static and therefore no object instance will be passed to it. This is equivalent to the Python statement:]]
]
``setattr(self, name, staticmethod(getattr(self, name)))``
[variablelist
[[Note][Attempting to invoke def(name,...) after invoking staticmethod(name) will [link raise] a RuntimeError.]]
[[Returns][`*this`]]
]
``
template <unspecified>
class_& def(detail::operator_<unspecified>);
``
[variablelist
[[Effects][Adds a Python [@http://www.python.org/doc/ref/specialnames.html special method] as described [link high_level_components.boost_python_operators_hpp here].]]
[[Returns][`*this`]]
]
``
template <class U>
class_& setattr(char const* name, U const& u);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]]
[[Effects][Converts `u` to Python and adds it to the attribute dictionary of the extension class:
``PyObject_SetAttrString(this->ptr(), name, object(u).ptr());``]]
[[Returns][`*this`]]
]
``
template <class Get>
void add_property(char const* name, Get const& fget, char const* doc=0);
template <class Get, class Set>
void add_property(
char const* name, Get const& fget, Set const& fset, char const* doc=0);
``
[variablelist
[[Requires][name is an [link ntbs] which conform to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]]
[[Effects][Creates a new Python [@http://www.python.org/2.2.2/descrintro.html#property property] class instance, passing `object(fget)` (and `object(fset)` in the second form) with an (optional) docstring `doc` to its constructor, then adds that property to the Python class object under construction with the given attribute name.]]
[[Returns][`*this`]]
[[Rationale][Allows users to easily expose functions that can be invoked from Python with attribute access syntax.]]
]
``
template <class Get>
void add_static_property(char const* name, Get const& fget);
template <class Get, class Set>
void add_static_property(char const* name, Get const& fget, Set const& fset);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]]
[[Effects][Creates a Boost.Python.StaticProperty object, passing `object(fget)` (and `object(fset)` in the second form) to its constructor, then adds that property to the Python class under construction with the given attribute name. StaticProperty is a special subclass of Python's property class which can be called without an initial self argument.]]
[[Returns][`*this`]]
[[Rationale][Allows users to easily expose functions that can be invoked from Python with static attribute access syntax.]]
]
``
template <class D>
class_& def_readonly(char const* name, D T::*pm, char const* doc=0);
template <class D>
class_& def_readonly(char const* name, D const& d);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules]. `doc` is also an [link ntbs].]]
[[Effects][``this->add_property(name, make_getter(pm), doc);`` and ``this->add_static_property(name, make_getter(d));`` respectively.]]
[[Returns][`*this`]]
[[Rationale][Allows users to easily expose a class' data member or free variable such that it can be inspected from Python with a natural syntax.]]
]
``
template <class D>
class_& def_readwrite(char const* name, D T::*pm, char const* doc=0);
template <class D>
class_& def_readwrite(char const* name, D& d);
``
[variablelist
[[Effects][``this->add_property(name, make_getter(pm), make_setter(pm), doc);`` and ``this->add_static_property(name, make_getter(d), make_setter(d));`` respectively.]]
[[Returns][`*this`]]
[[Rationale][Allows users to easily expose a class' data or free variable member such that it can be inspected and set from Python with a natural syntax.]]
]
``
template <typename PickleSuite>
class_& def_pickle(PickleSuite const&);
``
[variablelist
[[Requires][PickleSuite must be publically derived from [link topics.pickle_support.the_pickle_interface pickle_suite].]]
[[Effects][Defines a legal combination of the special attributes and methods: __getinitargs__, __getstate__, __setstate__, __getstate_manages_dict__, __safe_for_unpickling__, __reduce__]]
[[Returns][`*this`]]
[[Rationale][Provides an [link topics.pickle_support.the_pickle_interface easy to use high-level interface] for establishing complete [link topics.pickle_support.the_pickle_interface pickle support] for the wrapped class. The user is protected by compile-time consistency checks.]]
]
``class_& enable_pickling();``
[variablelist
[[Effects][Defines the __reduce__ method and the __safe_for_unpickling__ attribute.]]
[[Returns][`*this`]]
[[Rationale][Light-weight alternative to def_pickle(). Enables implementation of pickle support from Python.]]
]
[endsect]
[endsect]
[section Class template bases<T1, T2, ...TN>]
An MPL sequence which can be used in class_<...> instantiations indicate a list of base classes.
[section Class template bases synopsis]
``
namespace boost { namespace python
{
template <T1 = unspecified,...Tn = unspecified>
struct bases
{};
}}
``
[endsect]
[endsect]
[section Examples]
Given a C++ class declaration:
``
class Foo : public Bar, public Baz
{
public:
Foo(int x, char const* y);
Foo(double);
std::string const& name() { return m_name; }
void name(char const*);
double value; // public data
private:
...
};
``
A corresponding Boost.Python extension class can be created with:
``
using namespace boost::python;
class_<Foo,bases<Bar,Baz> >("Foo",
"This is Foo's docstring."
"It describes our Foo extension class",
init<int,char const*>(args("x","y"), "__init__ docstring")
)
.def(init<double>())
.def("get_name", &Foo::get_name, return_internal_reference<>())
.def("set_name", &Foo::set_name)
.def_readwrite("value", &Foo::value);
``
[endsect]
[endsect]

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[chapter High Level Components
[quickbook 1.7]
]
[include class.qbk]
[include def.qbk]
[include def_visitor.qbk]
[include docstring_options.qbk]
[include enum.qbk]
[include errors.qbk]
[include exception_translator.qbk]
[include init.qbk]
[include iterator.qbk]
[include module.qbk]
[include operators.qbk]
[include scope.qbk]
[include stl_iterator.qbk]
[include wrapper.qbk]

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[chapter Concepts
[quickbook 1.7]
]
[section CallPolicies]
[section Introduction]
Models of the CallPolicies concept are used to specialize the behavior of Python callable objects
generated by Boost.Python to wrapped C++ objects like function and member function pointers,
providing three behaviors:
# `precall` - Python argument tuple management before the wrapped object is invoked
# `result_converter` - C++ return value handling
# `postcall` - Python argument tuple and result management after the wrapped object is invoked
# `extract_return_type` - metafunction for extracting the return type from a given signature type sequence
[endsect]
[section CallPolicies Composition]
In order to allow the use of multiple models of CallPolicies in the same callable object,
Boost.Python's CallPolicies class templates provide a chaining interface which allows them to be
recursively composed. This interface takes the form of an optional template parameter, `Base`, which
defaults to `default_call_policies`. By convention, the `precall` function of the `Base` is invoked after
the `precall` function supplied by the `outer` template, and the `postcall` function of the `Base` is invoked
before the `postcall` function of the `outer` template. If a `result_converter` is supplied by the `outer`
template, it replaces any `result_converter` supplied by the `Base`. For an example, see
`return_internal_reference`.
[endsect]
[section Concept Requirements]
[table
[[Expression][Type][Result/Semantics]]
[[`x.precall(a)`][convertible to `bool`]
[returns `false` and `PyErr_Occurred() != 0` upon failure, `true` otherwise.]]
[[`P::result_converter`][A model of `ResultConverterGenerator`.]
[An MPL unary Metafunction Class used produce the "preliminary" result object.]]
[[`x.postcall(a, r)`][convertible to `PyObject*`]
[`0` and `PyErr_Occurred() != 0` upon failure. Must "conserve references" even in the event of an exception. In other words, if `r` is not returned, its reference count must be decremented; if another existing object is returned, its reference count must be incremented.]]
[[`P::extract_return_type`][A model of Metafunction.]
[An MPL unary Metafunction used extract the return type from a given signature. By default it is derived from `mpl::front`.]]
]
[endsect]
[endsect]
[section Dereferenceable]
[section Introduction]
Instances of a `Dereferenceable` type can be used like a pointer to access an lvalue.
[endsect]
[section Concept Requirements]
In the table below, `T` is a model of Dereferenceable, and `x` denotes an object of type `T`. In addition, all pointers are `Dereferenceable`.
[table
[[Expression][Result][Operational Semantics]]
[[`get_pointer(x)`][convertible to `pointee<T>::type*`]
[`&*x`, or a null pointer ]]
]
[endsect]
[endsect]
[section Extractor]
[section Introduction]
An Extractor is a class which Boost.Python can use to extract C++ objects from Python objects, and is typically used by facilities that define `from_python` conversions for "traditional" Python extension types.
[endsect]
[section Concept Requirements]
In the table below, `X` denotes a model of `Extractor` and `a` denotes an instance of a Python object type.
[table
[[Expression][Type][Semantics]]
[[`X::execute(a)`][non-void]
[Returns the C++ object being extracted. The execute function must not be overloaded.]]
[[`&a.ob_type`][`PyTypeObject**`]
[Points to the `ob_type` field of an object which is layout-compatible with `PyObject`]]
]
[endsect]
[section Notes]
Informally, an Extractor's execute member must be a non-overloaded static function whose single argument is a Python object type. Acceptable Python object types include those publicly (and unambiguously) derived from PyObject, and POD types which are layout-compatible with PyObject.
[endsect]
[endsect]
[section HolderGenerator]
[section Introduction]
A HolderGenerator is a unary metafunction class which returns types suitable for holding instances of its argument in a wrapped C++ class instance.
[endsect]
[section Concept Requirements]
In the table below, `G` denotes an type which models `HolderGenerator`, and `X` denotes a class type.
[table
[[Expression][Requirements]]
[[`G::apply<X>::type`][A concrete subclass of `instance_holder` which can hold objects of type `X`. ]]
]
[endsect]
[endsect]
[section ResultConverter]
[section Introduction]
A ResultConverter for a type `T` is a type whose instances can be used to convert C++ return values of type `T` `to_python`. A ResultConverterGenerator is an MPL unary metafunction class which, given the return type of a C++ function, returns a ResultConverter for that type. ResultConverters in Boost.Python generally inspect library's registry of converters to find a suitable converter, but converters which don't use the registry are also possible.
[endsect]
[section ResultConverter Concept Requirements]
In the table below, `C` denotes a ResultConverter type for a type `R`, `c` denotes an object of type `C`, and `r` denotes an object of type `R`.
[table
[[Expression][Type][Semantics]]
[[`C c`][]
[Constructs a `c` object.]]
[[`c.convertible()`][convertible to `bool`]
[`false` iff no conversion from any `R` value to a Python object is possible.]]
[[`c(r)`][convertible to `PyObject*`]
[A pointer to a Python object corresponding to `r`, or `0` iff `r` could not be converted `to_python`, in which case `PyErr_Occurred` should return non-zero.]]
[[`c.get_pytype()`][`PyTypeObject const *`]
[A pointer to a Python Type object corresponding to result of the conversion, or `0`. Used for documentation generation. If `0` is returned the generated type in the documentation will be object.]]
]
[endsect]
[section ResultConverterGenerator Concept Requirements]
In the table below, `G` denotes a ResultConverterGenerator type and `R` denotes a possible C++ function return type.
[table
[[Expression][Requirements]]
[[`G::apply<R>::type`][A ResultConverter type for `R`.]]
]
[endsect]
[endsect]
[section ObjectWrapper]
[section Introduction]
This page defines two concepts used to describe classes which manage a Python objects, and which are intended to support usage with a Python-like syntax.
[endsect]
[section ObjectWrapper Concept Requirements]
Models of the ObjectWrapper concept have [link object_wrappers.boost_python_object_hpp.class_object object] as a publicly-accessible base class, and are used to supply special construction behavior and/or additional convenient functionality through (often templated) member functions. Except when the return type R is itself an [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper], a member function invocation of the form ``x.some_function(a1, a2,...an)`` always has semantics equivalent to:
``extract<R>(x.attr("some_function")(object(a1), object(a2),...object(an)))()`` (see [link concepts.objectwrapper.caveat caveat] below).
[endsect]
[section TypeWrapper Concept Requirements]
TypeWrapper is a refinement of [link concepts.objectwrapper.objectwrapper_concept_requiremen ObjectWrapper] which is associated with a particular Python type `X`. For a given TypeWrapper `T`, a valid constructor expression ``T(a1, a2,...an)`` builds a new T object managing the result of invoking X with arguments corresponding to ``object(a1), object(a2),...object(an)``.
When used as arguments to wrapped C++ functions, or as the template parameter to [link to_from_python_type_conversion.boost_python_extract_hpp.class_template_extract extract<>], only instances of the associated Python type will be considered a match.
[endsect]
[section Caveat]
The upshot of the special member function invocation rules when the return type is a TypeWrapper is that it is possible for the returned object to manage a Python object of an inappropriate type. This is not usually a serious problem; the worst-case result is that errors will be detected at runtime a little later than they might otherwise be. For an example of how this can occur, note that the [link object_wrappers.boost_python_dict_hpp.class_dict dict] member function `items` returns an object of type [link object_wrappers.boost_python_list_hpp.class_list list]. Now suppose the user defines this `dict` subclass in Python:
``
>>> class mydict(dict):
... def items(self):
... return tuple(dict.items(self)) # return a tuple
``
Since an instance of `mydict` is also an instance of `dict`, when used as an argument to a wrapped C++ function, [link object_wrappers.boost_python_dict_hpp.class_dict boost::python::dict] can accept objects of Python type `mydict`. Invoking `items()` on this object can result in an instance of [link object_wrappers.boost_python_list_hpp.class_list boost::python::list] which actually holds a Python `tuple`. Subsequent attempts to use `list` methods (e.g. `append`, or any other mutating operation) on this object will raise the same exception that would occur if you tried to do it from Python.
[endsect]
[endsect]

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[chapter To/From Python Type Conversion
[quickbook 1.7]
]
[include extract.qbk]
[include implicit.qbk]
[include lvalue_from_pytype.qbk]
[include opaque_pointer_converter.qbk]
[include to_python_converter.qbk]
[include register_ptr_to_python.qbk]

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[section boost/python/copy_const_reference.hpp]
[section Class `copy_const_reference`]
`copy_const_reference` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning a reference-to-const type such that the referenced value is copied into a new Python object.
``
namespace boost { namespace python
{
struct copy_const_reference
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `copy_const_reference` metafunctions]
``template <class T> struct apply``
[variablelist
[[Requires][`T` is `U const&` for some `U`.]]
[[Returns][`typedef to_python_value<T> type;`]]
]
[endsect]
[section Example]
C++ module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/copy_const_reference.hpp>
#include <boost/python/return_value_policy.hpp>
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar const& get_bar() const { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_<Bar>("Bar");
class_<Foo>("Foo", init<int>())
.def("get_bar", &Foo::get_bar
, return_value_policy<copy_const_reference>())
;
}
``
Python code:
``
>>> from my_module import *
>>> f = Foo(3) # create a Foo object
>>> b = f.get_bar() # make a copy of the internal Bar object
``
[endsect]
[endsect]

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[section boost/python/copy_non_const_reference.hpp]
[section Class `copy_non_const_reference`]
`copy_non_const_reference` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning a reference-to-non-const type such that the referenced value is copied into a new Python object.
``
namespace boost { namespace python
{
struct copy_non_const_reference
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `copy_non_const_reference` metafunctions]
``template <class T> struct apply``
[variablelist
[[Requires][`T` is `U &` for some non-const `U`.]]
[[Returns][`typedef to_python_value<T> type`;]]
]
[endsect]
[section Example]
C++ module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/copy_non_const_reference.hpp>
#include <boost/python/return_value_policy.hpp>
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar& get_bar() { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_<Bar>("Bar");
class_<Foo>("Foo", init<int>())
.def("get_bar", &Foo::get_bar
, return_value_policy<copy_non_const_reference>())
;
}
``
Python code:
``
>>> from my_module import *
>>> f = Foo(3) # create a Foo object
>>> b = f.get_bar() # make a copy of the internal Bar object
``
[endsect]
[endsect]

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[section boost/python/data_members.hpp]
[section Introduction]
`make_getter()` and `make_setter()` are the functions used internally by [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu `class_<>::def_readonly`] and [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu `class_<>::def_readwrite`] to produce Python callable objects which wrap C++ data members.
[endsect]
[section Functions]
``
template <class C, class D>
object make_getter(D C::*pm);
template <class C, class D, class Policies>
object make_getter(D C::*pm, Policies const& policies);
``
[variablelist
[[Requires][Policies is a model of [link concepts.callpolicies `CallPolicies`].]]
[[Effects][Creates a Python callable object which accepts a single argument that can be converted from_python to C*, and returns the corresponding member D member of the C object, converted to_python. If policies is supplied, it will be applied to the function as described here. Otherwise, the library attempts to determine whether D is a user-defined class type, and if so uses return_internal_reference<>
for Policies. Note that this test may inappropriately choose return_internal_reference<> in some cases when D is a smart pointer type. This is a known defect.]]
[[Returns][An instance of object which holds the new Python callable object.]]
]
``
template <class D>
object make_getter(D const& d);
template <class D, class Policies>
object make_getter(D const& d, Policies const& policies);
template <class D>
object make_getter(D const* p);
template <class D, class Policies>
object make_getter(D const* p, Policies const& policies);
``
[variablelist
[[Requires][Policies is a model of CallPolicies.]]
[[Effects][Creates a Python callable object which accepts no arguments and returns d or *p, converted to_python on demand. If policies is supplied, it will be applied to the function as described here. Otherwise, the library attempts to determine whether D is a user-defined class type, and if so uses reference_existing_object for Policies.]]
[[Returns][An instance of object which holds the new Python callable object.]]
]
``
template <class C, class D>
object make_setter(D C::*pm);
template <class C, class D, class Policies>
object make_setter(D C::*pm, Policies const& policies);
``
[variablelist
[[Requires][Policies is a model of CallPolicies.]]
[[Effects][Creates a Python callable object which, when called from Python, expects two arguments which can be converted from_python to C* and D const&, respectively, and sets the corresponding D member of the C object. If policies is supplied, it will be applied to the function as described here.]]
[[Returns][An instance of object which holds the new Python callable object.]]
]
``
template <class D>
object make_setter(D& d);
template <class D, class Policies>
object make_setter(D& d, Policies const& policies);
template <class D>
object make_setter(D* p);
template <class D, class Policies>
object make_setter(D* p, Policies const& policies);
``
[variablelist
[[Requires][Policies is a model of CallPolicies.]]
[[Effects][Creates a Python callable object which accepts one argument, which is converted from Python to D const& and written into d or *p, respectively. If policies is supplied, it will be applied to the function as described here.]]
[[Returns][An instance of object which holds the new Python callable object.]]
]
[endsect]
[section Example]
The code below uses make_getter and make_setter to expose a data member as functions:
``
#include <boost/python/data_members.hpp>
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
struct X
{
X(int x) : y(x) {}
int y;
};
using namespace boost::python;
BOOST_PYTHON_MODULE_INIT(data_members_example)
{
class_<X>("X", init<int>())
.def("get", make_getter(&X::y))
.def("set", make_setter(&X::y))
;
}
``
It can be used this way in Python:
``
>>> from data_members_example import *
>>> x = X(1)
>>> x.get()
1
>>> x.set(2)
>>> x.get()
2
``
[endsect]
[endsect]

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[section boost/python/def.hpp]
[section Introduction]
`def()` is the function which can be used to expose C++ functions and callable objects as Python functions in the [link high_level_components.boost_python_scope_hpp.introduction current scope].
[endsect]
[section Functions]
``
template <class F>
void def(char const* name, F f);
template <class Fn, class A1>
void def(char const* name, Fn fn, A1 const&);
template <class Fn, class A1, class A2>
void def(char const* name, Fn fn, A1 const&, A2 const&);
template <class Fn, class A1, class A2, class A3>
void def(char const* name, Fn fn, A1 const&, A2 const&, A3 const&);
``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].
* If `Fn` is [derived from] [link object_wrappers.boost_python_object_hpp.class_object object], it will be added to the [link high_level_components.boost_python_scope_hpp.introduction current scope] as a single overload. To be useful, `fn` should be [@http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6 callable].
* If `a1` is the result of an [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions overload-dispatch-expression], only the second form is allowed and `fn` must be a pointer to function or pointer to member function whose [link arity] is the same as A1's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions maximum arity].
[*Effects:] For each prefix `P` of `Fn`\ 's sequence of argument types, beginning with the one whose length is `A1`\ 's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions minimum arity], adds a `name(...)` function overload to the [link high_level_components.boost_python_scope_hpp.introduction current scope]. Each overload generated invokes a1's call-expression with P, using a copy of a1's call policies. If the longest valid prefix of A1 contains N types and a1 holds M keywords, an initial sequence of the keywords are used for all but the first N - M arguments of each overload.
* Otherwise, fn must be a non-null function or member function pointer, and a single function overload built around fn is added to the current scope. If any of a1-a3 are supplied, they may be selected in any order from the table below.
[table
[[Mnemonic Name][Requirements/Type properties][Effects]]
[[docstring][Any [link ntbs]][Value will be bound to the `__doc__` attribute of the resulting method overload.]]
[[policies][A model of [link concepts.callpolicies CallPolicies]][A copy will be used as the call policies of the resulting method overload.]]
[[keywords][The result of a [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] specifying no more arguments than the [link arity] of `fn`.][A copy will be used as the call policies of the resulting method overload.]]
]
]]
]
[endsect]
[section Example]
``
#include <boost/python/def.hpp>
#include <boost/python/module.hpp>
#include <boost/python/args.hpp>
using namespace boost::python;
char const* foo(int x, int y) { return "foo"; }
BOOST_PYTHON_MODULE(def_test)
{
def("foo", foo, args("x", "y"), "foo's docstring");
}
``
[endsect]
[endsect]

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[section boost/python/def_visitor.hpp]
[section Introduction]
<boost/python/def_visitor.hpp> provides a generic visitation interface through which the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] def member functionality can be extended non-intrusively to avoid cluttering the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] interface. It declares the `def_visitor<T>` class template, which is parameterized on the derived type `DerivedVisitor`, which provides the actual `def` functionality through its `visit` member functions.
[endsect]
[section Class `def_visitor`]
The class `def_visitor` is a base class paramaterized by its derived class. The `def_visitor` class is a protocol class. Its derived class, DerivedVisitor, is expected to have a member function `visit`. The `def_visitor` class is never instantiated directly. Instead, an instance of its subclass, DerivedVisitor, is passed on as an argument to the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] `def` member function.
``
namespace boost { namespace python {
template <class DerivedVisitor>
class def_visitor {};
}
``
[variablelist
[[Requires][The client supplied class DerivedVisitor template parameter is expected to:
* be privately derived from def_visitor
* grant friend access to class def_visitor_access
* define either or both visit member functions listed in the table below:
[table
[[Expression][Return Type][Requirements][Effects]]
[[`visitor.visit(cls)`][`void`]
[`cls` is an instance of a [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] being wrapped to Python. `visitor` is a `def_visitor` derived class.]
[A call to `cls.def(visitor)` forwards to this member function.]]
[[`visitor.visit(cls, name, options)`][`void`]
[`cls` is a [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel class_] instance, name is a C string. `visitor` is a `def_visitor` derived class. options is a context specific optional argument.]
[A call to `cls.def(name, visitor)` or `cls.def(name, visitor, options)` forwards to this member function. ]]]
]]
]
[endsect]
[section Example]
``
class X {/*...*/};
class my_def_visitor : boost::python::def_visitor<my_def_visitor>
{
friend class def_visitor_access;
template <class classT>
void visit(classT& c) const
{
c.def("foo", &my_def_visitor::foo);
c.def("bar", &my_def_visitor::bar);
}
static void foo(X& self);
static void bar(X& self);
};
BOOST_PYTHON_MODULE(my_ext)
{
class_<X>("X")
.def(my_def_visitor());
}
``
[endsect]
[endsect]

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[section boost/python/default_call_policies.hpp]
[section Class `default_call_policies`]
`default_call_policies` is a model of [link concepts.callpolicies `CallPolicies`] with no `precall` or `postcall` behavior and a `result_converter` which handles by-value returns. Wrapped C++ functions and member functions `use default_call_policies` unless otherwise specified. You may find it convenient to derive new models of [link concepts.callpolicies `CallPolicies`] from `default_call_policies`.
``
namespace boost { namespace python
{
struct default_call_policies
{
static bool precall(PyObject*);
static PyObject* postcall(PyObject*, PyObject* result);
typedef default_result_converter result_converter;
template <class Sig> struct extract_return_type : mpl::front<Sig>{};
};
}}
``
[endsect]
[section Class `default_call_policies` static functions]
``bool precall(PyObject*);``
[variablelist
[[Returns][true]]
[[Throws][nothing]]
]
``PyObject* postcall(PyObject*, PyObject* result);``
[variablelist
[[Returns][result]]
[[Throws][nothing]]
]
[endsect]
[section Class `default_result_converter`]
default_result_converter is a model of [link concepts.resultconverter.resultconvertergenerator_concept `ResultConverterGenerator`] which can be used to wrap C++ functions returning non-pointer types, `char const*`, and `PyObject*`, by-value.
``
namespace boost { namespace python
{
struct default_result_converter
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `default_result_converter` metafunctions]
``template <class T> struct apply``
[variablelist
[[Requires][T is not a reference type. If T is a pointer type, T is const char* or PyObject*. ]]
[[Returns][typedef to_python_value<T const&> type;]]
]
[endsect]
[section Example]
This example comes from the Boost.Python implementation itself. Because the return_value_policy class template does not implement precall or postcall behavior, its default base class is default_call_policies:
``
template <class Handler, class Base = default_call_policies>
struct return_value_policy : Base
{
typedef Handler result_converter;
};
``
[endsect]
[endsect]

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[section boost/python/dict.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/dev/doc/devel/lib/typesmapping.html `dict`] type.
[endsect]
[section Class `dict`]
Exposes the [@http://www.python.org/dev/doc/devel/lib/typesmapping.html mapping protocol] of Python's built-in `dict` type. The semantics of the constructors and member functions defined below can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since `dict` is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `dict` instances as well.
``
namespace boost { namespace python
{
class dict : public object
{
dict();
template< class T >
dict(T const & data);
// modifiers
void clear();
dict copy();
template <class T1, class T2>
tuple popitem();
template <class T>
object setdefault(T const &k);
template <class T1, class T2>
object setdefault(T1 const & k, T2 const & d);
void update(object_cref E);
template< class T >
void update(T const & E);
// observers
list values() const;
object get(object_cref k) const;
template<class T>
object get(T const & k) const;
object get(object_cref k, object_cref d) const;
object get(T1 const & k, T2 const & d) const;
bool has_key(object_cref k) const;
template< class T >
bool has_key(T const & k) const;
list items() const;
object iteritems() const;
object iterkeys() const;
object itervalues() const;
list keys() const;
};
}}
``
[endsect]
[section Example]
``
using namespace boost::python;
dict swap_object_dict(object target, dict d)
{
dict result = extract<dict>(target.attr("__dict__"));
target.attr("__dict__") = d;
return result;
}
``
[endsect]
[endsect]

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[section boost/python/docstring_options.hpp]
[section Introduction]
Boost.Python supports user-defined docstrings with automatic appending of C++ signatures. These features are enabled by default. The class docstring_options is available to selectively suppress the user-defined docstrings, signatures, or both.
[endsect]
[section Class `docstring_options`]
Controls the appearance of docstrings of wrapped functions and member functions for the life-time of the instance. The instances are noncopyable to eliminate the possibility of surprising side effects.
``namespace boost { namespace python {
class docstring_options : boost::noncopyable
{
public:
docstring_options(bool show_all=true);
docstring_options(bool show_user_defined, bool show_signatures);
docstring_options(bool show_user_defined, bool show_py_signatures, bool show_cpp_signatures);
~docstring_options();
void disable_user_defined();
void enable_user_defined();
void disable_signatures();
void enable_signatures();
void disable_py_signatures();
void enable_py_signatures();
void disable_cpp_signatures();
void enable_cpp_signatures();
void disable_all();
void enable_all();
};
}}
``
[endsect]
[section Class dostring_options constructors]
``
docstring_options(bool show_all=true);
``
[variablelist
[[Effects][Constructs a docstring_options object which controls the appearance of function and member-function docstrings defined in the code that follows. If show_all is true, both the user-defined docstrings and the automatically generated Python and C++ signatures are shown. If show_all is false the `__doc__` attributes are `None`.]]
]
``
docstring_options(bool show_user_defined, bool show_signatures);
``
[variablelist
[[Effects][Constructs a `docstring_options` object which controls the appearance of function and member-function docstrings defined in the code that follows. Iff `show_user_defined` is `true`, the user-defined docstrings are shown. Iff `show_signatures` is `true`, Python and C++ signatures are automatically added. If both `show_user_defined` and `show_signatures` are `false`, the `__doc__` attributes are `None`.]]
]
``
docstring_options(bool show_user_defined, bool show_py_signatures, bool show_cpp_signatures);
``
[variablelist
[[Effects][Constructs a `docstring_options` object which controls the appearance of function and member-function docstrings defined in the code that follows. Iff `show_user_defined` is `true`, the user-defined docstrings are shown. Iff `show_py_signatures` is `true`, Python signatures are automatically added. Iff `show_cpp_signatures` is true, C++ signatures are automatically added. If all parameters are `false`, the `__doc__` attributes are `None`.]]
]
[endsect]
[section Class docstring_options destructor]
``~docstring_options();``
[variablelist
[[Effects][Restores the previous state of the docstring options. In particular, if `docstring_options` instances are in nested C++ scopes the settings effective in the enclosing scope are restored. If the last `docstring_options` instance goes out of scope the default "all on" settings are restored.]]]
[endsect]
[section Class `docstring_options` modifier functions]
``
void disable_user_defined();
void enable_user_defined();
void disable_signatures();
void enable_signatures();
void disable_py_signatures();
void enable_py_signatures();
void disable_cpp_signatures();
void enable_cpp_signatures();
void disable_all();
void enable_all();
``
These member functions dynamically change the appearance of docstrings in the code that follows. The `*_user_defined()` and `*_signatures()` member functions are provided for fine-grained control. The `*_all()` member functions are convenient shortcuts to manipulate all settings simultaneously.
[endsect]
[section Example]
[section Docstring options defined at compile time]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/docstring_options.hpp>
void foo() {}
BOOST_PYTHON_MODULE(demo)
{
using namespace boost::python;
docstring_options doc_options(DEMO_DOCSTRING_SHOW_ALL);
def("foo", foo, "foo doc");
}
``
If compiled with `-DDEMO_DOCSTRING_SHOW_ALL=true`:
``
>>> import demo
>>> print demo.foo.__doc__
foo() -> None : foo doc
C++ signature:
foo(void) -> void
``
If compiled with `-DDEMO_DOCSTRING_SHOW_ALL=false`:
``
>>> import demo
>>> print demo.foo.__doc__
None
``
[endsect]
[section Selective suppressions]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/args.hpp>
#include <boost/python/docstring_options.hpp>
int foo1(int i) { return i; }
int foo2(long l) { return static_cast<int>(l); }
int foo3(float f) { return static_cast<int>(f); }
int foo4(double d) { return static_cast<int>(d); }
BOOST_PYTHON_MODULE(demo)
{
using namespace boost::python;
docstring_options doc_options;
def("foo1", foo1, arg("i"), "foo1 doc");
doc_options.disable_user_defined();
def("foo2", foo2, arg("l"), "foo2 doc");
doc_options.disable_signatures();
def("foo3", foo3, arg("f"), "foo3 doc");
doc_options.enable_user_defined();
def("foo4", foo4, arg("d"), "foo4 doc");
doc_options.enable_py_signatures();
def("foo5", foo4, arg("d"), "foo5 doc");
doc_options.disable_py_signatures();
doc_options.enable_cpp_signatures();
def("foo6", foo4, arg("d"), "foo6 doc");
}
``
Python code:
``
>>> import demo
>>> print demo.foo1.__doc__
foo1( (int)i) -> int : foo1 doc
C++ signature:
foo1(int i) -> int
>>> print demo.foo2.__doc__
foo2( (int)l) -> int :
C++ signature:
foo2(long l) -> int
>>> print demo.foo3.__doc__
None
>>> print demo.foo4.__doc__
foo4 doc
>>> print demo.foo5.__doc__
foo5( (float)d) -> int : foo5 doc
>>> print demo.foo6.__doc__
foo6 doc
C++ signature:
foo6(double d) -> int
``
[endsect]
[section Wrapping from multiple C++ scopes]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/args.hpp>
#include <boost/python/docstring_options.hpp>
int foo1(int i) { return i; }
int foo2(long l) { return static_cast<int>(l); }
int bar1(int i) { return i; }
int bar2(long l) { return static_cast<int>(l); }
namespace {
void wrap_foos()
{
using namespace boost::python;
// no docstring_options here
// -> settings from outer C++ scope are in effect
def("foo1", foo1, arg("i"), "foo1 doc");
def("foo2", foo2, arg("l"), "foo2 doc");
}
void wrap_bars()
{
using namespace boost::python;
bool show_user_defined = true;
bool show_signatures = false;
docstring_options doc_options(show_user_defined, show_signatures);
def("bar1", bar1, arg("i"), "bar1 doc");
def("bar2", bar2, arg("l"), "bar2 doc");
}
}
BOOST_PYTHON_MODULE(demo)
{
boost::python::docstring_options doc_options(false);
wrap_foos();
wrap_bars();
}
``
Python code:
``
>>> import demo
>>> print demo.foo1.__doc__
None
>>> print demo.foo2.__doc__
None
>>> print demo.bar1.__doc__
bar1 doc
>>> print demo.bar2.__doc__
bar2 doc
``
[endsect]
[endsect]
[endsect]

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[chapter Embedding
[quickbook 1.7]
]
[include exec.qbk]
[include import.qbk]

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[section boost/python/enum.hpp]
[section Introduction]
<boost/python/enum.hpp> defines the interface through which users expose their C++ enumeration types to Python. It declares the `enum_` class template, which is parameterized on the enumeration type being exposed.
[endsect]
[section Class template `enum_`]
Creates a Python class derived from Python's `int` type which is associated with the C++ type passed as its first parameter.
``
namespace boost { namespace python
{
template <class T>
class enum_ : public object
{
enum_(char const* name, char const* doc = 0);
enum_<T>& value(char const* name, T);
enum_<T>& export_values();
};
}}
``
[endsect]
[section Class template `enum_` constructors]
``enum_(char const* name, char const* doc=0);``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]]
[[Effects][Constructs an `enum_` object holding a Python extension type derived from `int` which is named `name`. The named attribute of the [link high_level_components.boost_python_scope_hpp current scope] is bound to the new extension type.]]
]
[endsect]
[section Class template `enum_` modifier functions]
``enum_<T>& value(char const* name, T x);``
[variablelist
[[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]]
[[Effects][adds an instance of the wrapped enumeration type with value x to the type's dictionary as the named attribute.]]
[[Returns][`*this`]]
]
``enum_<T>& export_values();``
[variablelist
[[Effects][sets attributes in the [link high_level_components.boost_python_scope_hpp current scope] with the same names and values as all enumeration values exposed so far by calling value().]]
[[Returns][`*this`]]
]
[endsect]
[section Example]
C++ module definition
``
#include <boost/python/enum.hpp>
#include <boost/python/def.hpp>
#include <boost/python/module.hpp>
using namespace boost::python;
enum color { red = 1, green = 2, blue = 4 };
color identity_(color x) { return x; }
BOOST_PYTHON_MODULE(enums)
{
enum_<color>("color")
.value("red", red)
.value("green", green)
.export_values()
.value("blue", blue)
;
def("identity", identity_);
}
``
Interactive Python:
``
>>> from enums import *
>>> identity(red)
enums.color.red
>>> identity(color.red)
enums.color.red
>>> identity(green)
enums.color.green
>>> identity(color.green)
enums.color.green
>>> identity(blue)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
NameError: name 'blue' is not defined
>>> identity(color.blue)
enums.color.blue
>>> identity(color(1))
enums.color.red
>>> identity(color(2))
enums.color.green
>>> identity(color(3))
enums.color(3)
>>> identity(color(4))
enums.color.blue
>>> identity(1)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: bad argument type for built-in operation
``
[endsect]
[endsect]

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[section boost/python/errors.hpp]
[section Introduction]
<boost/python/errors.hpp> provides types and functions for managing and translating between Python and C++ exceptions. This is relatively low-level functionality that is mostly used internally by Boost.Python. Users should seldom need it.
[endsect]
[section Class `error_already_set`]
error_already_set is an exception type which can be thrown to indicate that a Python error has occurred. If thrown, the precondition is that [@http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71 PyErr_Occurred()] returns a value convertible to `true`. Portable code shouldn't throw this exception type directly, but should instead use [link high_level_components.boost_python_errors_hpp.functions throw_error_already_set()], below.
``
namespace boost { namespace python
{
class error_already_set {};
}}
``
[endsect]
[section Functions]
``
template <class T> bool handle_exception(T f) throw();
void handle_exception() throw();
``
[variablelist
[[Requires][The first form requires that the expression function0<void>(f) is valid. The second form requires that a C++ exception is currently being handled (see section 15.1 in the C++ standard).]]
[[Effects][The first form calls f() inside a try block which first attempts to use all registered [link high_level_components.boost_python_exception_translato exception translators]. If none of those translates the exception, the catch clauses then set an appropriate Python exception for the C++ exception caught, returning true if an exception was thrown, false otherwise. The second form passes a function which rethrows the exception currently being handled to the first form.]]
[[Postconditions][No exception is being handled]]
[[Throws][nothing]]
[[Rationale][At inter-language boundaries it is important to ensure that no C++ exceptions escape, since the calling language usually doesn't have the equipment necessary to properly unwind the stack. Use handle_exception to manage exception translation whenever your C++ code is called directly from the Python API. This is done for you automatically by the usual function wrapping facilities: [link function_invocation_and_creation.boost_python_make_function_hpp.functions make_function()], [link function_invocation_and_creation.boost_python_make_function_hpp.functions make_constructor()], [link high_level_components.boost_python_def_hpp.functions def()] and [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu class_::def()]. The second form can be more convenient to use (see the example below), but various compilers have problems when exceptions are rethrown from within an enclosing try block.]]
]
``template <class T> T* expect_non_null(T* x);``
[variablelist
[[Returns][x]]
[[Throws][error_already_set() iff x == 0.]]
[[Rationale][Simplifies error-handling when calling functions in the Python/C API which return 0 on error.]]
]
``void throw_error_already_set();``
[variablelist
[[Effects][throw error_already_set();]]
[[Rationale][Simplifies error-handling when calling functions in the Python/C API which return 0 on error.]]
]
``void throw_error_already_set();``
[variablelist
[[Effects][throw error_already_set();]]
[[Rationale][Many platforms and compilers are not able to consistently catch exceptions thrown across shared library boundaries. Using this function from the Boost.Python library ensures that the appropriate catch block in handle_exception() can catch the exception.]]
]
[endsect]
[section Example]
``
#include <string>
#include <boost/python/errors.hpp>
#include <boost/python/object.hpp>
#include <boost/python/handle.hpp>
// Returns a std::string which has the same value as obj's "__name__"
// attribute.
std::string get_name(boost::python::object obj)
{
// throws if there's no __name__ attribute
PyObject* p = boost::python::expect_non_null(
PyObject_GetAttrString(obj.ptr(), "__name__"));
char const* s = PyString_AsString(p);
if (s != 0)
Py_DECREF(p);
// throws if it's not a Python string
std::string result(
boost::python::expect_non_null(
PyString_AsString(p)));
Py_DECREF(p); // Done with p
return result;
}
//
// Demonstrate form 1 of handle_exception
//
// Place into result a Python Int object whose value is 1 if a and b have
// identical "__name__" attributes, 0 otherwise.
void same_name_impl(PyObject*& result, boost::python::object a, boost::python::object b)
{
result = PyInt_FromLong(
get_name(a) == get_name(a2));
}
object borrowed_object(PyObject* p)
{
return boost::python::object(
boost::python::handle<>(
boost::python::borrowed(a1)));
}
// This is an example Python 'C' API interface function
extern "C" PyObject*
same_name(PyObject* args, PyObject* keywords)
{
PyObject* a1;
PyObject* a2;
PyObject* result = 0;
if (!PyArg_ParseTuple(args, const_cast<char*>("OO"), &a1, &a2))
return 0;
// Use boost::bind to make an object compatible with
// boost::Function0<void>
if (boost::python::handle_exception(
boost::bind<void>(same_name_impl, boost::ref(result), borrowed_object(a1), borrowed_object(a2))))
{
// an exception was thrown; the Python error was set by
// handle_exception()
return 0;
}
return result;
}
//
// Demonstrate form 2 of handle_exception. Not well-supported by all
// compilers.
//
extern "C" PyObject*
same_name2(PyObject* args, PyObject* keywords)
{
PyObject* a1;
PyObject* a2;
PyObject* result = 0;
if (!PyArg_ParseTuple(args, const_cast<char*>("OO"), &a1, &a2))
return 0;
try {
return PyInt_FromLong(
get_name(borrowed_object(a1)) == get_name(borrowed_object(a2)));
}
catch(...)
{
// If an exception was thrown, translate it to Python
boost::python::handle_exception();
return 0;
}
}
``
[endsect]
[endsect]

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[section boost/python/exception_translator.hpp]
[section Introduction]
As described [link high_level_components.boost_python_errors_hpp.introduction here], it is important to make sure that exceptions thrown by C++ code do not pass into the Python interpreter core. By default, Boost.Python translates all C++ exceptions thrown by wrapped functions and module init functions into Python, but the default translators are extremely limited: most C++ exceptions will appear in Python as a [@http://www.python.org/doc/current/lib/module-exceptions.html RuntimeError] exception whose representation is 'Unidentifiable C++ Exception'. To produce better error messages, users can register additional exception translators as described below.
[endsect]
[section Function `register_exception_translator`]
``
template<class ExceptionType, class Translate>
void register_exception_translator(Translate translate);
``
[variablelist
[[Requires][Translate is CopyConstructible, and the following code must be well-formed:
``void f(ExceptionType x) { translate(x); }``.
The expression `translate(x)` must either throw a C++ exception, or a subsequent call to `PyErr_Occurred()` must return 1. ]]
[[Effects][Adds a copy of translate to the sequence of exception translators tried when Boost.Python catches an exception that is about to pass into Python's core interpreter. The new translator will get "first shot" at translating all exceptions matching the catch clause shown above. Any subsequently-registered translators will be allowed to translate the exception earlier. A translator which cannot translate a given C++ exception can re-throw it, and it will be handled by a translator which was registered earlier (or by the default translator).]]
]
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/exception_translator.hpp>
#include <exception>
struct my_exception : std::exception
{
char const* what() throw() { return "One of my exceptions"; }
};
void translate(my_exception const& e)
{
// Use the Python 'C' API to set up an exception object
PyErr_SetString(PyExc_RuntimeError, e.what());
}
void something_which_throws()
{
...
throw my_exception();
...
}
BOOST_PYTHON_MODULE(exception_translator_ext)
{
using namespace boost::python;
register_exception_translator<my_exception>(&translate);
def("something_which_throws", something_which_throws);
}
``
[endsect]
[endsect]

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[section boost/python/exec.hpp]
[section Introduction]
Exposes a mechanism for embedding the python interpreter into C++ code.
[endsect]
[section Function `eval`]
``
object eval(str expression,
object globals = object(),
object locals = object());
``
[variablelist
[[Effects][Evaluate Python expression from expression in the context specified by the dictionaries globals and locals. ]]
[[Returns][An instance of object which holds the value of the expression.]]
]
[endsect]
[section Function `exec`]
``
object exec(str code,
object globals = object(),
object locals = object());
``
[variablelist
[[Effects][Execute Python source code from code in the context specified by the dictionaries globals and locals. ]]
[[Returns][ An instance of object which holds the result of executing the code. ]]
]
[endsect]
[section Function `exec_file`]
``
object exec_file(str filename,
object globals = object(),
object locals = object());
``
[variablelist
[[Effects][Execute Python source code from the file named by filename in the context specified by the dictionaries globals and locals.]]
[[Returns][An instance of object which holds the result of executing the code. ]]
]
[endsect]
[section Examples]
The following example demonstrates the use of import and exec to define a function in python, and later call it from within C++.
``
#include <iostream>
#include <string>
using namespace boost::python;
void greet()
{
// Retrieve the main module.
object main = import("__main__");
// Retrieve the main module's namespace
object global(main.attr("__dict__"));
// Define greet function in Python.
object result = exec(
"def greet(): \n"
" return 'Hello from Python!' \n",
global, global);
// Create a reference to it.
object greet = global["greet"];
// Call it.
std::string message = extract<std::string>(greet());
std::cout << message << std::endl;
}
``
Instead of embedding the python script into a string, we could also store it in an a file...
``
def greet():
return 'Hello from Python!'
``
... and execute that instead.
``
// ...
// Load the greet function from a file.
object result = exec_file(script, global, global);
// ...
}
``
[endsect]
[endsect]

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[section boost/python/extract.hpp]
[section Introduction]
Exposes a mechanism for extracting C++ object values from generalized Python objects. Note that `extract<...>` can also be used to "downcast" an [link object_wrappers.boost_python_object_hpp.class_object `object`] to some specific [link concepts.objectwrapper ObjectWrapper]. Because invoking a mutable python type with an argument of the same type (e.g. `list([1,2]`) typically makes a copy of the argument object, this may be the only way to access the [link concepts.objectwrapper ObjectWrapper]\ 's interface on the original object.
[endsect]
[section Class template `extract`]
`extract<T>` can be used to extract a value of an arbitrary C++ type from an instance of [link object_wrappers.boost_python_object_hpp.class_object object]. Two usages are supported:
# `extract<T>(o)` is a temporary object which is implicitly convertible to `T` (explicit conversion is also available through the object's function-call operator). However, if no conversion is available which can convert o to an object of type `T`, a Python TypeError exception will be raised.
# `extract<T> x(o);` constructs an extractor whose `check()` member function can be used to ask whether a conversion is available without causing an exception to be thrown.
``
namespace boost { namespace python
{
template <class T>
struct extract
{
typedef unspecified result_type;
extract(PyObject*);
extract(object const&);
result_type operator()() const;
operator result_type() const;
bool check() const;
};
}}
``
[endsect]
[section Class template `extract` constructors and destructor]
``
extract(PyObject* p);
extract(object const&);
``
[variablelist
[[Requires][The first form requires that p is non-null.]]
[[Effects][Stores a pointer to the Python object managed by its constructor argument. In particular, the reference count of the object is not incremented. The onus is on the user to be sure it is not destroyed before the extractor's conversion function is called.]]
]
[endsect]
[section Class template `extract` observer functions]
``
result_type operator()() const;
operator result_type() const;
``
[variablelist
[[Effects][Converts the stored pointer to result_type, which is either T or T const&. ]]
[[Returns][An object of result_type corresponding to the one referenced by the stored pointer.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set `error_already_set`] and sets a `TypeError` if no such conversion is available. May also emit other unspecified exceptions thrown by the converter which is actually used.]]
]
`` bool check() const;``
[variablelist
[[Postconditions][None. In particular, note that a return value of true does not preclude an exception being thrown from operator result_type() or operator()().]]
[[Returns][false only if no conversion from the stored pointer to T is available.]]
]
[endsect]
[section Example]
``
#include <cstdio>
using namespace boost::python;
int Print(str s)
{
// extract a C string from the Python string object
char const* c_str = extract<char const*>(s);
// Print it using printf
std::printf("%s\n", c_str);
// Get the Python string's length and convert it to an int
return extract<int>(s.attr("__len__")())
}
``
The following example shows how extract can be used along with [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel `class_<...>`] to create and access an instance of a wrapped C++ class.
``
struct X
{
X(int x) : v(x) {}
int value() { return v; }
private:
int v;
};
BOOST_PYTHON_MODULE(extract_ext)
{
object x_class(
class_<X>("X", init<int>())
.def("value", &X::value))
;
// Instantiate an X object through the Python interface.
// Its lifetime is now managed by x_obj.
object x_obj = x_class(3);
// Get a reference to the C++ object out of the Python object
X& x = extract<X&>(x_obj);
assert(x.value() == 3);
}
``
[endsect]
[endsect]

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[section boost/python/function_doc_signature.hpp]
[section Introduction]
Boost.Python supports docstrings with automatic appending of Pythonic and C++ signatures. This feature is implemented by class `function_doc_signature_generator`. The class uses all of the overloads, supplied arg names and default values, as well as the user-defined docstrings, to generate documentation for a given function.
[endsect]
[section Class `function_doc_signature_generator`]
The class has only one public function which returns a list of strings documenting the overloads of a function.
``
namespace boost { namespace python { namespace objects {
class function_doc_signature_generator
{
public:
static list function_doc_signatures(function const *f);
};
}}}
``
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/args.hpp>
#include <boost/python/tuple.hpp>
#include <boost/python/class.hpp>
#include <boost/python/overloads.hpp>
#include <boost/python/raw_function.hpp>
using namespace boost::python;
tuple f(int x = 1, double y = 4.25, char const* z = "wow")
{
return make_tuple(x, y, z);
}
BOOST_PYTHON_FUNCTION_OVERLOADS(f_overloads, f, 0, 3)
struct X
{
tuple f(int x = 1, double y = 4.25, char const* z = "wow")
{
return make_tuple(x, y, z);
}
};
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(X_f_overloads, X::f, 0, 3)
tuple raw_func(tuple args, dict kw)
{
return make_tuple(args, kw);
}
BOOST_PYTHON_MODULE(args_ext)
{
def("f", f, (arg("x")=1, arg("y")=4.25, arg("z")="wow")
, "This is f's docstring"
);
def("raw", raw_function(raw_func));
def("f1", f, f_overloads("f1's docstring", args("x", "y", "z")));
class_<X>("X", "This is X's docstring", init<>(args("self")))
.def("f", &X::f
, "This is X.f's docstring"
, args("self","x", "y", "z"))
;
}
``
Python code: [python]
``
>>> import args_ext
>>> help(args_ext)
Help on module args_ext:
NAME
args_ext
FILE
args_ext.pyd
CLASSES
Boost.Python.instance(__builtin__.object)
X
class X(Boost.Python.instance)
| This is X's docstring
|
| Method resolution order:
| X
| Boost.Python.instance
| __builtin__.object
|
| Methods defined here:
|
| __init__(...)
| __init__( (object)self) -> None :
| C++ signature:
| void __init__(struct _object *)
|
| f(...)
| f( (X)self, (int)x, (float)y, (str)z) -> tuple : This is X.f's docstring
| C++ signature:
| class boost::python::tuple f(struct X {lvalue},int,double,char const *)
|
| .................
|
FUNCTIONS
f(...)
f([ (int)x=1 [, (float)y=4.25 [, (str)z='wow']]]) -> tuple : This is f's docstring
C++ signature:
class boost::python::tuple f([ int=1 [,double=4.25 [,char const *='wow']]])
f1(...)
f1([ (int)x [, (float)y [, (str)z]]]) -> tuple : f1's docstring
C++ signature:
class boost::python::tuple f1([ int [,double [,char const *]]])
raw(...)
object raw(tuple args, dict kwds) :
C++ signature:
object raw(tuple args, dict kwds)
``
[endsect]
[endsect]

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[chapter Function Invocation and Creation
[quickbook 1.7]
]
[include args.qbk]
[include call.qbk]
[include call_method.qbk]
[include data_members.qbk]
[include make_function.qbk]
[include overloads.qbk]
[include ptr.qbk]
[include raw_function.qbk]
[section Function documentation]
[include function_doc_signature.qbk]
[include pytype_function.qbk]
[endsect]
[section Models of CallPolicies]
[include default_call_policies.qbk]
[include return_arg.qbk]
[include return_internal_reference.qbk]
[include return_value_policy.qbk]
[include with_custodian_and_ward.qbk]
[endsect]
[section Models of ResultConverter]
[include to_python_indirect.qbk]
[include to_python_value.qbk]
[endsect]
[section Models of ResultConverterGenerator]
[include copy_const_reference.qbk]
[include copy_non_const_reference.qbk]
[include manage_new_object.qbk]
[include reference_existing_object.qbk]
[include return_by_value.qbk]
[include return_opaque_pointer.qbk]
[endsect]

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[section boost/python/handle.hpp]
[section Introduction]
<boost/python/handle.hpp> provides class template `handle`, a smart pointer for managing reference-counted Python objects.
[endsect]
[section Class template `handle`]
`handle` is a smart pointer to a Python object type; it holds a pointer of type `T*`, where `T` is its template parameter. T must be either a type derived from `PyObject` or a [link pod POD] type whose initial `sizeof(PyObject)` bytes are layout-compatible with `PyObject`. Use `handle<>` at the boundary between the Python/'C' API and high-level code; prefer object for a generalized interface to Python objects.
In this document, the term "upcast" refers to an operation which converts a pointer `Y*` to a base class `pointer T*` via `static_cast<T*>` if `Y` is derived from `T`, or via C-style cast (`T*`) if it is not. However, in the latter case the "upcast" is ill-formed if the initial `sizeof(PyObject)` bytes of `Y` are not layout-compatible with `PyObject`.
``
namespace boost { namespace python
{
template <class T>
class handle
{
typedef unspecified-member-function-pointer bool_type;
public: // types
typedef T element_type;
public: // member functions
~handle();
template <class Y>
explicit handle(detail::borrowed<null_ok<Y> >* p);
template <class Y>
explicit handle(null_ok<detail::borrowed<Y> >* p);
template <class Y>
explicit handle(detail::borrowed<Y>* p);
template <class Y>
explicit handle(null_ok<Y>* p);
template <class Y>
explicit handle(Y* p);
handle();
handle& operator=(handle const& r);
template<typename Y>
handle& operator=(handle<Y> const & r); // never throws
template <typename Y>
handle(handle<Y> const& r);
handle(handle const& r);
T* operator-> () const;
T& operator* () const;
T* get() const;
void reset();
T* release();
operator bool_type() const; // never throws
private:
T* m_p;
};
template <class T> struct null_ok;
namespace detail { template <class T> struct borrowed; }
}}
``
[section Class template `handle` constructors and destructor]
``virtual ~handle();``
[variablelist
[[Effects][`Py_XDECREF(upcast<PyObject*>(m_p))`]]
]
``template <class Y>
explicit handle(detail::borrowed<null_ok<Y> >* p);
``
[variablelist
[[Effects][
``Py_XINCREF(upcast<PyObject*>(p));
m_p = upcast<T*>(p);
``
]]
]
``template <class Y>
explicit handle(null_ok<detail::borrowed<Y> >* p);``
[variablelist
[[Effects][
``Py_XINCREF(upcast<PyObject*>(p));
m_p = upcast<T*>(p);
``
]]
]
``template <class Y>
explicit handle(detail::borrowed<Y>* p);``
[variablelist
[[Effects][
``Py_XINCREF(upcast<PyObject*>(p));
m_p = upcast<T*>(expect_non_null(p));
``
]]
]
``template <class Y>
explicit handle(null_ok<Y>* p);
``
[variablelist
[[Effects][`m_p = upcast<T*>(p);`]]
]
``
template <class Y>
explicit handle(Y* p);
``
[variablelist
[[Effects][`m_p = upcast<T*>(expect_non_null(p));`]]
]
``
handle();
``
[variablelist
[[Effects][`m_p = 0;`]]
]
``
template <typename Y>
handle(handle<Y> const& r);
handle(handle const& r);
``
[variablelist
[[Effects][m_p = r.m_p; Py_XINCREF(upcast<PyObject*>(m_p));]]
]
[endsect]
[section Class template `handle` modifiers]
``
handle& operator=(handle const& r);
template<typename Y>
handle& operator=(handle<Y> const & r); // never throws
``
[variablelist
[[Effects][`Py_XINCREF(upcast<PyObject*>(r.m_p)); Py_XDECREF( upcast<PyObject*>(m_p)); m_p = r.m_p;`]]
]
``
T* release();
``
[variablelist
[[Effects][`T* x = m_p; m_p = 0; return x;`]]
]
``
void reset();
``
[variablelist
[[Effects][`*this = handle<T>();`]]
]
[endsect]
[section Class template `handle` observers]
``
T* operator-> () const;
T* get() const;
``
[variablelist
[[Returns][`m_p;`]]
]
``
T& operator* () const;
``
[variablelist
[[Returns][`*m_p;`]]
]
``
operator bool_type() const; // never throws
``
[variablelist
[[Returns][`0` if `m_p == 0`, a pointer convertible to true otherwise.]]
]
[endsect]
[endsect]
[section Function `borrowed`]
``
template <class T>
detail::borrowed<T>* borrowed(T* p)
{
return (detail::borrowed<T>*)p;
}
``
[endsect]
[section Function `allow_null`]
``
template <class T>
null_ok<T>* allow_null(T* p)
{
return (null_ok<T>*)p;
}
``
[endsect]
[endsect]

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[section boost/python/has_back_reference.hpp]
[section Introduction]
<boost/python/has_back_reference.hpp> defines the predicate metafunction `has_back_reference<>`, which can be specialized by the user to indicate that a wrapped class instance holds a `PyObject*` corresponding to a Python object.
[endsect]
[section Class template `has_back_reference`]
A unary metafunction whose value is true iff its argument is a `pointer_wrapper<>`.
``
namespace boost { namespace python
{
template<class WrappedClass> class has_back_reference
{
typedef mpl::false_ type;
};
}}
``
A metafunction that is inspected by Boost.Python to determine how wrapped classes can be constructed.
`type::value` is an integral constant convertible to bool of unspecified type.
Specializations may substitute a true-valued integral constant wrapper for type iff for each invocation of `class_<WrappedClass>::def(init< type-sequence...>())` and the implicitly wrapped copy constructor (unless it is noncopyable), there exists a corresponding constructor `WrappedClass::WrappedClass(PyObject*, type-sequence...)`. If such a specialization exists, the WrappedClass constructors will be called with a "back reference" pointer to the corresponding Python object whenever they are invoked from Python. The easiest way to provide this nested type is to derive the specialization from `mpl::true_`.
[endsect]
[section Examples]
In C++:
``
#include <boost/python/class.hpp>
#include <boost/python/module.hpp>
#include <boost/python/has_back_reference.hpp>
#include <boost/python/handle.hpp>
#include <boost/shared_ptr.hpp>
using namespace boost::python;
using boost::shared_ptr;
struct X
{
X(PyObject* self) : m_self(self), m_x(0) {}
X(PyObject* self, int x) : m_self(self), m_x(x) {}
X(PyObject* self, X const& other) : m_self(self), m_x(other.m_x) {}
handle<> self() { return handle<>(borrowed(m_self)); }
int get() { return m_x; }
void set(int x) { m_x = x; }
PyObject* m_self;
int m_x;
};
// specialize has_back_reference for X
namespace boost { namespace python
{
template <>
struct has_back_reference<X>
: mpl::true_
{};
}}
struct Y
{
Y() : m_x(0) {}
Y(int x) : m_x(x) {}
int get() { return m_x; }
void set(int x) { m_x = x; }
int m_x;
};
shared_ptr<Y>
Y_self(shared_ptr<Y> self) { return self; }
BOOST_PYTHON_MODULE(back_references)
{
class_<X>("X")
.def(init<int>())
.def("self", &X::self)
.def("get", &X::get)
.def("set", &X::set)
;
class_<Y, shared_ptr<Y> >("Y")
.def(init<int>())
.def("get", &Y::get)
.def("set", &Y::set)
.def("self", Y_self)
;
}
``
The following Python session illustrates that x.self() returns the same Python object on which it is invoked, while y.self() must create a new Python object which refers to the same Y instance.
In Python:
``
>>> from back_references import *
>>> x = X(1)
>>> x2 = x.self()
>>> x2 is x
1
>>> (x.get(), x2.get())
(1, 1)
>>> x.set(10)
>>> (x.get(), x2.get())
(10, 10)
>>>
>>>
>>> y = Y(2)
>>> y2 = y.self()
>>> y2 is y
0
>>> (y.get(), y2.get())
(2, 2)
>>> y.set(20)
>>> (y.get(), y2.get())
(20, 20)
``
[endsect]
[endsect]

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[section boost/python/implicit.hpp]
[section Introduction]
`implicitly_convertible` allows Boost.Python to implicitly take advantage of a C++ implicit or explicit conversion when matching Python objects to C++ argument types.
[endsect]
[section Function template `implicit_convertible`]
``
template <class Source, class Target>
void implicitly_convertible();
``
[table
[[Parameter][Description]]
[[Source][The source type of the implicit conversion]]
[[Target][The target type of the implicit conversion]]
]
[variablelist
[[Requires][The declaration `Target t(s);`, where s is of type Source, is valid.]]
[[Effects][registers an rvalue `from_python` converter to Target which can succeed for any `PyObject* p` iff there exists any registered converter which can produce Source rvalues]]
[[Rationale][C++ users expect to be able to take advantage of the same sort of interoperability in Python as they do in C++.]]
]
[endsect]
[section Example]
In C++:
``
#include <boost/python/class.hpp>
#include <boost/python/implicit.hpp>
#include <boost/python/module.hpp>
using namespace boost::python;
struct X
{
X(int x) : v(x) {}
operator int() const { return v; }
int v;
};
int x_value(X const& x)
{
return x.v;
}
X make_x(int n) { return X(n); }
BOOST_PYTHON_MODULE(implicit_ext)
{
def("x_value", x_value);
def("make_x", make_x);
class_<X>("X",
init<int>())
;
implicitly_convertible<X,int>();
implicitly_convertible<int,X>();
}
``
In Python:
``
>>> from implicit_ext import *
>>> x_value(X(42))
42
>>> x_value(42)
42
>>> x = make_x(X(42))
>>> x_value(x)
42
``
[endsect]
[endsect]

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[section boost/python/import.hpp]
[section Introduction]
Exposes a mechanism for importing python modules.
[endsect]
[section Function `import`]
``object import(str name);``
[variablelist
[[Effects][Imports the module named by name.]]
[[Returns][An instance of object which holds a reference to the imported module.]]
]
[endsect]
[section Examples]
The following example demonstrates the use of import to access a function in python, and later call it from within C++.
``
#include <iostream>
#include <string>
using namespace boost::python;
void print_python_version()
{
// Load the sys module.
object sys = import("sys");
// Extract the python version.
std::string version = extract<std::string>(sys.attr("version"));
std::cout << version << std::endl;
}
``
[endsect]
[endsect]

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[section Indexing support]
[section Introduction]
Indexing is a `Boost Python` facility for easy exportation of indexable C++ containers to Python. Indexable containers are containers that allow random access through the `operator[]` (e.g. `std::vector`).
While `Boost Python` has all the facilities needed to expose indexable C++ containers such as the ubiquitous std::vector to Python, the procedure is not as straightforward as we'd like it to be. Python containers do not map easily to C++ containers. Emulating Python containers in C++ (see Python Reference Manual, [@http://www.python.org/doc/current/ref/sequence-types.html Emulating container types]) using `Boost.Python` is non trivial. There are a lot of issues to consider before we can map a C++ container to Python. These involve implementing wrapper functions for the methods `__len__`, `__getitem__`, `__setitem__`, `__delitem__`, `__iter__` and `__contains__`.
The goals:
* Make indexable C++ containers behave exactly as one would expect a Python container to behave.
* Provide default reference semantics for container element indexing (`__getitem__`) such that c[i] can be mutable. Require:
``
val = c[i]
c[i].m()
val == c[i]
``
where m is a non-const (mutating) member function (method).
* Return safe references from `__getitem__` such that subsequent adds and deletes to and from the container will not result in dangling references (will not crash Python).
* Support slice indexes.
* Accept Python container arguments (e.g. `lists`, `tuples`) wherever appropriate.
* Allow for extensibility through re-definable policy classes.
* Provide predefined support for the most common STL and STL-like indexable containers.
[endsect]
[section The Indexing Interface]
The `indexing_suite` class is the base class for the management of C++ containers intended to be integrated to Python. The objective is make a C++ container look and feel and behave exactly as we'd expect a Python container. The class automatically wraps these special Python methods (taken from the Python reference: Emulating container types):
[variablelist
[[__len__(self)]
[Called to implement the built-in function `len()`. Should return the length of the object, an integer `>= 0`. Also, an object that doesn't define a `__nonzero__()` method and whose `__len__()` method returns zero is considered to be false in a Boolean context.]]
[[__getitem__(self, key)]
[Called to implement evaluation of `self[key]`. For sequence types, the accepted keys should be integers and slice objects. Note that the special interpretation of negative indexes (if the class wishes to emulate a sequence type) is up to the `__getitem__()` method. If key is of an inappropriate type, `TypeError` may be raised; if of a value outside the set of indexes for the sequence (after any special interpretation of negative values), IndexError should be raised. [Note: for loops expect that an IndexError will be raised for illegal indexes to allow proper detection of the end of the sequence.]]]
[[__setitem__(self, key, value)]
[Called to implement assignment to self[key]. Same note as for __getitem__(). This should only be implemented for mappings if the objects support changes to the values for keys, or if new keys can be added, or for sequences if elements can be replaced. The same exceptions should be raised for improper key values as for the __getitem__() method.]]
[[__delitem__(self, key)]
[Called to implement deletion of self[key]. Same note as for __getitem__(). This should only be implemented for mappings if the objects support removal of keys, or for sequences if elements can be removed from the sequence. The same exceptions should be raised for improper key values as for the __getitem__() method.]]
[[__iter__(self)]
[This method is called when an iterator is required for a container. This method should return a new iterator object that can iterate over all the objects in the container. For mappings, it should iterate over the keys of the container, and should also be made available as the method iterkeys().
Iterator objects also need to implement this method; they are required to return themselves. For more information on iterator objects, see [@https://docs.python.org/3/library/stdtypes.html#iterator-types Iterator Types] in the [@https://docs.python.org/3/library/index.html Python Library Reference].]]
[[__contains__(self, item)]
[Called to implement membership test operators. Should return true if item is in self, false otherwise. For mapping objects, this should consider the keys of the mapping rather than the values or the key-item pairs.]]
]
[endsect]
[section index_suite sub-classes]
The `indexing_suite` is not meant to be used as is. A couple of policy functions must be supplied by subclasses of `indexing_suite`. However, a set of indexing_suite subclasses for the standard indexable STL containers will be provided, In most cases, we can simply use the available predefined suites. In some cases, we can refine the predefined suites to suit our needs.
[section vector_index_suite]
The `vector_indexing_suite` class is a predefined `indexing_suite` derived class designed to wrap `std::vector` (and `std::vector`-like [i.e. a class with `std::vector` interface]) classes. It provides all the policies required by the `indexing_suite`.
Example usage:
``
class X {...};
...
class_<std::vector<X> >("XVec")
.def(vector_indexing_suite<std::vector<X> >())
;
``
XVec is now a full-fledged Python container (see the example in full, along with its python test).
[endsect]
[section map_index_suite]
The `map_indexing_suite` class is a predefined `indexing_suite` derived class designed to wrap `std::map` (and `std::map`-like [i.e. a class with `std::map` interface]) classes. It provides all the policies required by the `indexing_suite`.
Example usage:
``
class X {...};
...
class_<std::map<X> >("XMap")
.def(map_indexing_suite<std::map<X> >())
;
``
By default indexed elements are returned by proxy. This can be disabled by supplying `true` in the `NoProxy` template parameter. XMap is now a full-fledged Python container (see the example in full, along with its python test).
[endsect]
[endsect]
[section `indexing_suite` class]
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[Container][A class type][ The container type to be wrapped to Python. ][]]
[[DerivedPolicies][A subclass of indexing_suite][ Derived classes provide the policy hooks. See DerivedPolicies below. ][]]
[[NoProxy][A boolean][ By default indexed elements have Python reference semantics and are returned by proxy. This can be disabled by supplying true in the NoProxy template parameter. ][false]]
[[NoSlice][A boolean][ Do not allow slicing. ][false]]
[[Data][][The container's data type.][Container::value_type]]
[[Index][][The container's index type.][Container::size_type]]
[[Key][][The container's key type.][Container::value_type]]
]
``
template <class Container,
class DerivedPolicies,
bool NoProxy = false,
bool NoSlice = false,
class Data = typename Container::value_type,
class Index = typename Container::size_type,
class Key = typename Container::value_type>
class indexing_suite : unspecified
{
public:
indexing_suite(); // default constructor
}
``
[section DerivedPolicies]
Derived classes provide the hooks needed by the indexing_suite:
``
data_type&
get_item(Container& container, index_type i);
static object
get_slice(Container& container, index_type from, index_type to);
static void
set_item(Container& container, index_type i, data_type const& v);
static void
set_slice(
Container& container, index_type from,
index_type to, data_type const& v
);
template <class Iter>
static void
set_slice(Container& container, index_type from,
index_type to, Iter first, Iter last
);
static void
delete_item(Container& container, index_type i);
static void
delete_slice(Container& container, index_type from, index_type to);
static size_t
size(Container& container);
template <class T>
static bool
contains(Container& container, T const& val);
static index_type
convert_index(Container& container, PyObject* i);
static index_type
adjust_index(index_type current, index_type from,
index_type to, size_type len);
``
Most of these policies are self explanatory. However, convert_index and adjust_index deserve some explanation.
convert_index converts a Python index into a C++ index that the container can handle. For instance, negative indexes in Python, by convention, start counting from the right(e.g. C[-1] indexes the rightmost element in C). convert_index should handle the necessary conversion for the C++ container (e.g. convert -1 to C.size()-1). convert_index should also be able to convert the type of the index (A dynamic Python type) to the actual type that the C++ container expects.
When a container expands or contracts, held indexes to its elements must be adjusted to follow the movement of data. For instance, if we erase 3 elements, starting from index 0 from a 5 element vector, what used to be at index 4 will now be at index 1:
``
[a][b][c][d][e] ---> [d][e]
^ ^
4 1
``
adjust_index takes care of the adjustment. Given a current index, the function should return the adjusted index when data in the container at index from..to is replaced by len elements.
[endsect]
[endsect]
[section class `vector_indexing_suite`]
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[Container][A class type][ The container type to be wrapped to Python. ][]]
[[NoProxy][A boolean][ By default indexed elements have Python reference semantics and are returned by proxy. This can be disabled by supplying true in the NoProxy template parameter. ][false]]
[[DerivedPolicies][A subclass of indexing_suite][ The vector_indexing_suite may still be derived to further tweak any of the predefined policies. Static polymorphism through CRTP (James Coplien. "Curiously Recurring Template Pattern". C++ Report, Feb. 1995) enables the base indexing_suite class to call policy function of the most derived class ][]]
]
``
template <class Container,
bool NoProxy = false,
class DerivedPolicies = unspecified_default>
class vector_indexing_suite : unspecified_base
{
public:
typedef typename Container::value_type data_type;
typedef typename Container::value_type key_type;
typedef typename Container::size_type index_type;
typedef typename Container::size_type size_type;
typedef typename Container::difference_type difference_type;
data_type&
get_item(Container& container, index_type i);
static object
get_slice(Container& container, index_type from, index_type to);
static void
set_item(Container& container, index_type i, data_type const& v);
static void
set_slice(Container& container, index_type from,
index_type to, data_type const& v);
template <class Iter>
static void
set_slice(Container& container, index_type from,
index_type to, Iter first, Iter last);
static void
delete_item(Container& container, index_type i);
static void
delete_slice(Container& container, index_type from, index_type to);
static size_t
size(Container& container);
static bool
contains(Container& container, key_type const& key);
static index_type
convert_index(Container& container, PyObject* i);
static index_type
adjust_index(index_type current, index_type from,
index_type to, size_type len);
};
``
[endsect]
[section class `map_indexing_suite`]
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[Container][ A class type ][ The container type to be wrapped to Python. ][]]
[[NoProxy][ A boolean ][ By default indexed elements have Python reference semantics and are returned by proxy. This can be disabled by supplying true in the NoProxy template parameter. ][ false ]]
[[DerivedPolicies][ A subclass of indexing_suite ][ The vector_indexing_suite may still be derived to further tweak any of the predefined policies. Static polymorphism through CRTP (James Coplien. "Curiously Recurring Template Pattern". C++ Report, Feb. 1995) enables the base indexing_suite class to call policy function of the most derived class ][]]
]
``
template <class Container,
bool NoProxy = false,
class DerivedPolicies = unspecified_default>
class map_indexing_suite : unspecified_base
{
public:
typedef typename Container::value_type value_type;
typedef typename Container::value_type::second_type data_type;
typedef typename Container::key_type key_type;
typedef typename Container::key_type index_type;
typedef typename Container::size_type size_type;
typedef typename Container::difference_type difference_type;
static data_type&
get_item(Container& container, index_type i);
static void
set_item(Container& container, index_type i, data_type const& v);
static void
delete_item(Container& container, index_type i);
static size_t
size(Container& container);
static bool
contains(Container& container, key_type const& key);
static bool
compare_index(Container& container, index_type a, index_type b);
static index_type
convert_index(Container& container, PyObject* i);
};
``
[endsect]
[endsect]

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[section boost/python/init.hpp]
[section Introduction]
<boost/python/init.hpp> defines the interface for exposing C++ constructors to Python as extension class `__init__` functions.
[section init-expressions]
An init-expression is used to describe a family of `__init__` methods to be generated for an extension class, and the result has the following properties:
[variablelist
[[docstring][An [link ntbs] whose value will bound to the method's `__doc__` attribute]]
[[keywords][A [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] which will be used to name (a trailing subsequence of) the arguments to the generated `__init__` function(s).]]
[[call_policies][An instance of a model of [link concepts.callpolicies CallPolicies].]]
[[argument_types][An MPL sequence of C++ argument types which will be used to construct the wrapped C++ object. An init expression has one or more valid prefixes which are given by a sequence of prefixes of its argument types.]]
]
[endsect]
[endsect]
[section Class template `init`]
A MPL sequence which can be used to specify a family of one or more __init__ functions. Only the last Ti supplied may be an instantiation of optional<...>.
``
namespace boost { namespace python
{
template <T1 = unspecified,...Tn = unspecified>
struct init
{
init(char const* doc = 0);
template <class Keywords> init(Keywords const& kw, char const* doc = 0);
template <class Keywords> init(char const* doc, Keywords const& kw);
template <class CallPolicies>
unspecified operator[](CallPolicies const& policies) const
};
}}
``
[section Class template `init` constructors]
``
init(char const* doc = 0);
template <class Keywords> init(Keywords const& kw, char const* doc = 0);
template <class Keywords> init(char const* doc, Keywords const& kw);
``
[variablelist
[[Requires][If supplied, doc is an [link ntbs]. If supplied, kw is the result of a ]]
[[Effects][The result is an init-expression whose docstring is doc and whose keywords are a reference to kw. If the first form is used, the resulting expression's keywords are empty. The expression's call policies are an instance of [link function_invocation_and_creation.models_of_callpolicies.boost_python_default_call_polici default_call_policies]. If Tn is [link high_level_components.boost_python_init_hpp.class_template_optional optional<U1, U2,... Um>], the expression's valid prefixes are given by: ``(T1, T2,...Tn-1), (T1, T2,...Tn-1 , U1), (T1, T2,...Tn-1 , U1, U2), ...(T1, T2,...Tn-1 , U1, U2,...Um)``.
Otherwise, the expression has one valid prefix given by the template arguments the user specified. ]]
]
[endsect]
[section Class template `init` observer functions]
``
template <class Policies>
unspecified operator[](Policies const& policies) const
``
[variablelist
[[Requires][Policies is a model of [link concepts.callpolicies CallPolicies].]]
[[Effects][Returns a new [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] with all the same properties as the init object except that its call policies are replaced by a reference to policies.]]
]
[endsect]
[endsect]
[section Class template `optional` ]
A MPL sequence which can be used to specify the optional arguments to an __init__ function.
``
namespace boost { namespace python
{
template <T1 = unspecified,...Tn = unspecified>
struct optional {};
}}
``
[endsect]
[section Example]
Given the C++ declarations:
``
class Y;
class X
{
public:
X(int x, Y* y) : m_y(y) {}
X(double);
private:
Y* m_y;
};
``
A corresponing Boost.Python extension class can be created with:
``
using namespace boost::python;
class_<X>("X", "This is X's docstring.",
init<int,char const*>(args("x","y"), "X.__init__'s docstring")[
with_custodian_and_ward<1,3>()]
)
.def(init<double>())
;
``
[endsect]
[endsect]

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[section boost/python/instance_holder.hpp]
[section Introduction]
<boost/python/instance_holder.hpp> provides class `instance_holder`, the base class for types which hold C++ instances of wrapped classes.
[endsect]
[section Class template `instance_holder`]
`instance_holder` is an abstract base class whose concrete derived classes hold C++ class instances within their Python object wrappers. To allow multiple inheritance in Python from C++ class wrappers, each such Python object contains a chain of instance_holders. When an `__init__` function for a wrapped C++ class is invoked, a new `instance_holder` instance is created and installed in the Python object using its `install()` function. Each concrete class derived from `instance_holder` must provide a `holds()` implementation which allows Boost.Python to query it for the type(s) it is holding. In order to support the held type's wrapped constructor(s), the class must also provide constructors that can accept an initial `PyObject*` argument referring to the owning Python object, and which forward the rest of their arguments to the constructor of the held type. The initial argument is needed to enable virtual function overriding in Python, and may be ignored, depending on the specific `instance_holder` subclass.
``
namespace boost { namespace python
{
class instance_holder : noncopyable
{
public:
// destructor
virtual ~instance_holder();
// instance_holder modifiers
void install(PyObject* inst) throw();
// instance_holder observers
virtual void* holds(type_info) = 0;
};
}}
``
[section Class `intance_holder` destructor]
``virtual ~instance_holder();``
[variablelist
[[Effects][destroys the object]]
]
[endsect]
[section Class `intance_holder` modifiers]
``void install(PyObject* inst) throw();``
[variablelist
[[Requires][`inst` is a Python instance of a wrapped C++ class type, or is a type derived from a wrapped C++ class type. ]]
[[Effects][installs the new instance at the head of the Python object's chain of held instances. ]]
[[Throws][nothing]]
]
[endsect]
[section Class `intance_holder` observers]
``virtual void *holds(type_info x) = 0;``
[variablelist
[[Returns][A pointer to an object of the type described by `x` if `*this` contains such an object, 0 otherwise. ]]
]
[endsect]
[endsect]
[section Examples]
The following is a simplified version of the instance holder template used by Boost.Python to wrap classes held by smart pointers:
``
template <class SmartPtr, class Value>
struct pointer_holder : instance_holder
{
// construct from the SmartPtr type
pointer_holder(SmartPtr p)
:m_p(p)
// Forwarding constructors for the held type
pointer_holder(PyObject*)
:m_p(new Value())
{
}
template<class A0>
pointer_holder(PyObject*,A0 a0)
:m_p(new Value(a0))
{
}
template<class A0,class A1>
pointer_holder(PyObject*,A0 a0,A1 a1)
:m_p(new Value(a0,a1))
{
}
...
private: // required holder implementation
void* holds(type_info dst_t)
{
// holds an instance of the SmartPtr type...
if (dst_t == python::type_id<SmartPtr>())
return &this->m_p;
// ...and an instance of the SmartPtr's element_type, if the
// pointer is non-null
return python::type_id<Value>() == dst_t ? &*this->m_p : 0;
}
private: // data members
SmartPtr m_p;
};
``
[endsect]
[endsect]

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[section boost/python/iterator.hpp]
[section Introduction]
<boost/python/iterator.hpp> provides types and functions for creating [@http://www.python.org/doc/current/lib/typeiter.html Python iterators] from C++ Containers and Iterators. Note that if your `class_` supports random-access iterators, implementing [@http://www.python.org/doc/current/ref/sequence-types.html#l2h-128 __getitem__] (also known as the Sequence Protocol) may serve you better than using this facility: Python will automatically create an iterator type for you (see [@http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-35 `iter()`]), and each access can be range-checked, leaving no possiblity of accessing through an invalidated C++ iterator.
[endsect]
[section Class template `iterator`]
Instances of `iterator<C,P>` hold a reference to a callable Python object which, when invoked from Python, expects a single argument c convertible to C and creates a Python iterator that traverses `[c.begin(), c.end())`. The optional [link concepts.callpolicies CallPolicies] `P` can be used to control how elements are returned during iteration.
In the table below, c is an instance of Container.
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[Container][`[c.begin(),c.end()`) is a valid Iterator range.][The result will convert its argument to c and call c.begin() and c.end() to acquire iterators. To invoke Container's const `begin()` and `end()` functions, make it const.][ ]]
[[NextPolicies][A default-constructible model of [link concepts.callpolicies CallPolicies].][Applied to the resulting iterators' `next()` method.][An unspecified model of [link concepts.callpolicies CallPolicies] which always makes a copy of the result of deferencing the underlying C++ iterator]]
]
``
namespace boost { namespace python
{
template <class Container, class NextPolicies = unspecified>
struct iterator : object
{
iterator();
};
}}
``
[endsect]
[section Class template iterator constructors]
``iterator()``
[variablelist
[[Effects][Initializes its base class with the result of:
``range<NextPolicies>(&iterators<Container>::begin, &iterators<Container>::end)``]]
[[Postconditions][`this->get()` points to a Python callable object which creates a Python iterator as described above.]]
[[Rationale][Provides an easy way to create iterators for the common case where a C++ class being wrapped provides `begin()` and `end()`.]]
]
[endsect]
[section Class template `iterators`]
A utility class template which provides a way to reliably call its argument's `begin()` and `end()` member functions. Note that there is no portable way to take the address of a member function of a C++ standard library container, so `iterators<>` can be particularly helpful when wrapping them.
In the table below, x is an instance of C.
[table
[[Required Valid Expression][Type]]
[[x.begin()][Convertible to C::const_iterator if C is a const type; convertible to C::iterator otherwise.]]
[[x.end()][Convertible to C::const_iterator if C is a const type; convertible to C::iterator otherwise.]]
]
``
namespace boost { namespace python
{
template <class C>
struct iterators
{
typedef typename C::const_iterator iterator;
static iterator begin(C& x);
static iterator end(C& x);
};
}}
``
[endsect]
[section Class template iterators nested types]
If C is a const type,``typedef typename C::const_iterator iterator;``
Otherwise: ``typedef typename C::iterator iterator;``
[endsect]
[section Class template iterators static functions]
``static iterator begin(C&);``
[variablelist [[Returns][`x.begin()`]]]
``static iterator end(C&);``
[variablelist [[Returns][`x.end()`]]]
[endsect]
[section Functions]
``
template <class NextPolicies, class Target, class Accessor1, class Accessor2>
object range(Accessor1 start, Accessor2 finish);
template <class NextPolicies, class Accessor1, class Accessor2>
object range(Accessor1 start, Accessor2 finish);
template <class Accessor1, class Accessor2>
object range(Accessor1 start, Accessor2 finish);
``
[variablelist
[[Requires][ NextPolicies is a default-constructible model of [link concepts.callpolicies CallPolicies].]]
[[Effects][The first form creates a Python callable object which, when invoked, converts its argument to a Target object x, and creates a Python iterator which traverses `[bind(start,_1)(x), bind(finish,_1)(x))`, applying NextPolicies to the iterator's `next()` function.
The second form is identical to the first, except that Target is deduced from Accessor1 as follows:
# If Accessor1 is a function type, Target is the type of its first argument.
# If Accessor1 is a data member pointer of the form `R (T::*)`, Target is identical to `T`.
# If Accessor1 is a member function pointer of the form `R (T::*)(arguments...) cv-opt`, where cv-opt is an optional cv-qualifier, Target is identical to `T`.
The third form is identical to the second, except that NextPolicies is an unspecified model of [link concepts.callpolicies CallPolicies] which always makes a copy of the result of deferencing the underlying C++ iterator
]]
[[Rationale][The use of `boost::bind()` allows C++ iterators to be accessed through functions, member functions or data member pointers. Customization of NextPolicies (e.g. using [link function_invocation_and_creation.models_of_callpolicies.boost_python_return_internal_ref.class_template_return_internal_r return_internal_reference]) is useful when it is expensive to copy sequence elements of a wrapped class type. Customization of Target is useful when Accessor1 is a function object, or when a base class of the intended target type would otherwise be deduced.]]
]
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <vector>
using namespace boost::python;
BOOST_PYTHON_MODULE(demo)
{
class_<std::vector<double> >("dvec")
.def("__iter__", iterator<std::vector<double> >())
;
}
``
[endsect]
[endsect]

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[section boost_python_list.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/doc/current/lib/typesseq-mutable.html list] type.
[endsect]
[section Class `list`]
Exposes the [@http://www.python.org/doc/current/lib/typesseq-mutable.html mapping protocol] of Python's built-in `list` type. The semantics of the constructors and member functions defined below can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since `list` is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `list` instances as well.``
namespace boost { namespace python
{
class list : public object
{
public:
list(); // new list
template <class T>
explicit list(T const& sequence);
template <class T>
void append(T const& x);
template <class T>
long count(T const& value) const;
template <class T>
void extend(T const& x);
template <class T>
long index(T const& x) const;
template <class T>
void insert(object const& index, T const& x); // insert object before index
object pop(); // remove and return item at index (default last)
object pop(long index);
object pop(object const& index);
template <class T>
void remove(T const& value);
void reverse(); // reverse *IN PLACE*
void sort(); // sort *IN PLACE*; if given, cmpfunc(x, y) -> -1, 0, 1
template <class T>
void sort(T const& value);
};
}}
``
[endsect]
[section Example]
``
using namespace boost::python;
// Return the number of zeroes in the list
long zeroes(list l)
{
return l.count(0);
}
``
[endsect]
[endsect]

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[section boost/python/long.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/doc/current/lib/typesnumeric.html long] integer type.
[endsect]
[section Class `long_`]
Exposes the [@http://www.python.org/doc/current/lib/typesnumeric.html numeric type protocol] of Python's built-in `long` type. The semantics of the constructors and member functions defined below can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since `long_` is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `long_` instances as well.
``
namespace boost { namespace python
{
class long_ : public object
{
public:
long_(); // new long_
template <class T>
explicit long_(T const& rhs);
template <class T, class U>
long_(T const& rhs, U const& base);
};
}}
``
[endsect]
[section Example]
``
namespace python = boost::python;
// compute a factorial without overflowing
python::long_ fact(long n)
{
if (n == 0)
return python::long_(1);
else
return n * fact(n - 1);
}
``
[endsect]
[endsect]

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[section boost/python/lvalue_from_pytype.hpp]
[section Introduction]
<boost/python/lvalue_from_pytype.hpp> supplies a facility for extracting C++ objects from within Python instances of a given type. This is typically useful for dealing with "traditional" Python extension types.
[endsect]
[section Class template `lvalue_from_pytype`]
Class template lvalue_from_pytype will register from_python converters which, given an object of the given Python type, can extract references and pointers to a particular C++ type. Its template arguments are:
In the table below, x denotes an object of type PythonObject&
[table
[[Parameter][Requirements][Semantics]]
[[Extractor][a model of [link concepts.extractor `Extractor`] whose execute function returns a reference type.][Extracts the lvalue from the Python object once its type has been confirmed]]
[[python_type][A compile-time constant [@http://www.python.org/doc/2.2/ext/dnt-type-methods.html `PyTypeObject*`]][The Python type of instances convertible by this converter. Python subtypes are also convertible.]]
]
``
namespace boost { namespace python
{
template <class Extractor, PyTypeObject const* python_type>
struct lvalue_from_pytype
{
lvalue_from_pytype();
};
}}
``
[section Class template `lvalue_from_pytype` constructor]
``lvalue_from_pytype();``
[variablelist
[[Effects][Registers converters which can convert Python objects of the given type to lvalues of the type returned by Extractor::execute.]]
]
[endsect]
[endsect]
[section Class template `extract_identity`]
extract_identity is a model of [link concepts.extractor `Extractor`] which can be used in the common case where the C++ type to be extracted is the same as the Python object type.
``
namespace boost { namespace python
{
template <class InstanceType>
struct extract_identity
{
static InstanceType& execute(InstanceType& c);
};
}}
``
[section Class template `extract_identity` static functions]
``InstanceType& execute(InstanceType& c);``
[variablelist
[[Returns][c]]
]
[endsect]
[endsect]
[section Class template `extract_member`]
`extract_member` is a model of [link concepts.extractor `Extractor`] which can be used in the common case in the common case where the C++ type to be extracted is a member of the Python object.
``
namespace boost { namespace python
{
template <class InstanceType, class MemberType, MemberType (InstanceType::*member)>
struct extract_member
{
static MemberType& execute(InstanceType& c);
};
}}
``
[section Class template `extract_member` static functions]
``static MemberType& execute(InstanceType& c);``
[variablelist
[[Returns][`c.*member`]]
]
[endsect]
[endsect]
[section Example]
This example presumes that someone has implemented the standard noddy example module from the Python documentation, and we want to build a module which manipulates Noddys. Since noddy_NoddyObject is so simple that it carries no interesting information, the example is a bit contrived: it assumes you want to keep track of one particular object for some reason. This module would have to be dynamically linked to the module which defines noddy_NoddyType.
In C++:
``
#include <boost/python/module.hpp>
#include <boost/python/handle.hpp>
#include <boost/python/borrowed.hpp>
#include <boost/python/lvalue_from_pytype.hpp>
// definition lifted from the Python docs
typedef struct {
PyObject_HEAD
} noddy_NoddyObject;
using namespace boost::python;
static handle<noddy_NoddyObject> cache;
bool is_cached(noddy_NoddyObject* x)
{
return x == cache.get();
}
void set_cache(noddy_NoddyObject* x)
{
cache = handle<noddy_NoddyObject>(borrowed(x));
}
BOOST_PYTHON_MODULE(noddy_cache)
{
def("is_cached", is_cached);
def("set_cache", set_cache);
// register Noddy lvalue converter
lvalue_from_pytype<extract_identity<noddy_NoddyObject>,&noddy_NoddyType>();
}
``
In Python:
``
>>> import noddy
>>> n = noddy.new_noddy()
>>> import noddy_cache
>>> noddy_cache.is_cached(n)
0
>>> noddy_cache.set_cache(n)
>>> noddy_cache.is_cached(n)
1
>>> noddy_cache.is_cached(noddy.new_noddy())
0
``
[endsect]
[endsect]

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[section boost/python/make_function.hpp]
[section Introduction]
make_function() and make_constructor() are the functions used internally by def() and class_<>::def() to produce Python callable objects which wrap C++ functions and member functions.
[endsect]
[section Functions]
``
template <class F>
object make_function(F f)
template <class F, class Policies>
object make_function(F f, Policies const& policies)
template <class F, class Policies, class KeywordsOrSignature>
object make_function(F f, Policies const& policies, KeywordsOrSignature const& ks)
template <class F, class Policies, class Keywords, class Signature>
object make_function(F f, Policies const& policies, Keywords const& kw, Signature const& sig)
``
[variablelist
[[Requires][F is a function pointer or member function pointer type. If policies are supplied, it must be a model of CallPolicies. If kewords are supplied, it must be the result of a keyword-expression specifying no more arguments than the arity of f.]]
[[Effects][Creates a Python callable object which, when called from Python, converts its arguments to C++ and calls f. If F is a pointer-to-member-function type, the target object of the function call (*this) will be taken from the first Python argument, and subsequent Python arguments will be used as the arguments to f.
* If policies are supplied, it will be applied to the function as described here.
* If keywords are supplied, the keywords will be applied in order to the final arguments of the resulting function.
* If Signature is supplied, it should be an instance of an MPL front-extensible sequence representing the function's return type followed by its argument types. Pass a Signature when wrapping function object types whose signatures can't be deduced, or when you wish to override the types which will be passed to the wrapped function. ]]
[[Returns][An instance of object which holds the new Python callable object.]]
[[Caveats][An argument of pointer type may be 0 if None is passed from Python. An argument type which is a constant reference may refer to a temporary which was created from the Python object for just the duration of the call to the wrapped function, for example a std::vector conjured up by the conversion process from a Python list. Use a non-const reference argument when a persistent lvalue is required. ]]
]
``
template <class F>
object make_constructor(F f)
template <class F, class Policies>
object make_constructor(F f, Policies const& policies)
template <class F, class Policies, class KeywordsOrSignature>
object make_constructor(F f, Policies const& policies, KeywordsOrSignature const& ks)
template <class F, class Policies, class Keywords, class Signature>
object make_constructor(F f, Policies const& policies, Keywords const& kw, Signature const& sig)
``
[variablelist
[[Requires][F is a function pointer type. If policies are supplied, it must be a model of CallPolicies. If kewords are supplied, it must be the result of a keyword-expression specifying no more arguments than the arity of f.]]
[[Effects][Creates a Python callable object which, when called from Python, converts its arguments to C++ and calls f.]]
[[Returns][An instance of object which holds the new Python callable object.]]
]
[endsect]
[section Example]
C++ function exposed below returns a callable object wrapping one of two functions.
``
#include <boost/python/make_function.hpp>
#include <boost/python/module.hpp>
char const* foo() { return "foo"; }
char const* bar() { return "bar"; }
using namespace boost::python;
object choose_function(bool selector)
{
if (selector)
return boost::python::make_function(foo);
else
return boost::python::make_function(bar);
}
BOOST_PYTHON_MODULE(make_function_test)
{
def("choose_function", choose_function);
}
``
It can be used this way in Python:
``
>>> from make_function_test import *
>>> f = choose_function(1)
>>> g = choose_function(0)
>>> f()
'foo'
>>> g()
'bar'
``
[endsect]
[endsect]

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[section boost/python/manage_new_object.hpp]
[section Class `manage_new_object`]
`manage_new_object` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions which return a pointer to an object allocated with a new-expression, and expect the caller to take responsibility for deleting that object.
``
namespace boost { namespace python
{
struct manage_new_object
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `manage_new_object` metafunctions]
``template <class T> struct apply``
[variablelist
[[Requires][`T` is `U*` for some `U`.]]
[[Returns][`typedef to_python_indirect<T> type;`]]
]
[endsect]
[section Example]
In C++:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/manage_new_object.hpp>
#include <boost/python/return_value_policy.hpp>
struct Foo {
Foo(int x) : x(x){}
int get_x() { return x; }
int x;
};
Foo* make_foo(int x) { return new Foo(x); }
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
def("make_foo", make_foo, return_value_policy<manage_new_object>())
class_<Foo>("Foo")
.def("get_x", &Foo::get_x)
;
}
``
Python code:
``
>>> from my_module import *
>>> f = make_foo(3) # create a Foo object
>>> f.get_x()
3
``
[endsect]
[endsect]

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[section boost/python/module.hpp]
[section Introduction]
This header provides the basic facilities needed to create a Boost.Python extension module.
[endsect]
[section Macros]
`BOOST_PYTHON_MODULE(name)` is used to declare Python [@http://www.python.org/doc/2.2/ext/methodTable.html#SECTION003400000000000000000 module initialization functions]. The name argument must exactly match the name of the module to be initialized, and must conform to Python's [@http://www.python.org/doc/2.2/ref/identifiers.html identifier naming rules]. Where you would normally write
``
extern "C" void initname()
{
...
}
``
Boost.Python modules should be initialized with
``
BOOST_PYTHON_MODULE(name)
{
...
}
``
This macro generates two functions in the scope where it is used: `extern "C" void initname()`, and `void init_module_name()`, whose body must follow the macro invocation. `init_name` passes `init_module_name` to [link high_level_components.boost_python_errors_hpp.functions handle_exception()] so that any C++ exceptions generated are safely processeed. During the body of `init_name`, the [link high_level_components.boost_python_scope_hpp current scope] refers to the module being initialized.
[endsect]
[section Examples]
C++ module definition:
``
#include <boost/python/module.hpp>
BOOST_PYTHON_MODULE(xxx)
{
throw "something bad happened"
}
``
Interactive Python:
``
>>> import xxx
Traceback (most recent call last):
File "", line 1, in ?
RuntimeError: Unidentifiable C++ Exception
``
[endsect]
[endsect]

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[section boost/python/object.hpp]
[section Introduction]
Exposes the generic Python object wrapper class object, and related classes. In order to avoid some potenential problems with argument-dependent lookup and the generalized operators defined on object, all these facilities are defined in namespace boost::python::api, and object is imported into namespace boost::python with a using-declaration.
[endsect]
[section Class `slice_nil`]
``
class slice_nil;
static const _ = slice_nil();
``
A type that can be used to get the effect of leaving out an index in a Python slice expression:
``
>>> x[:-1]
>>> x[::-1]
``
C++ equivalent:
``
x.slice(_,-1)
x[slice(_,_,-1)]
``
[endsect]
[section Class `const_attribute_policies`]
The policies which are used for proxies representing an attribute access to a const object.
``
namespace boost { namespace python { namespace api
{
struct const_attribute_policies
{
typedef char const* key_type;
static object get(object const& target, char const* key);
};
}}}
``
[endsect]
[section Class `const_attribute_policies` static functions]
``
static object get(object const& target, char const* key);
``
[variablelist
[[Requires][key is an [link ntbs].]]
[[Effects][accesses the attribute of target named by key.]]
[[Returns][An object managing the result of the attribute access.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `attribute_policies`]
The policies which are used for proxies representing an attribute access to a mutable object.
``
namespace boost { namespace python { namespace api
{
struct attribute_policies : const_attribute_policies
{
static object const& set(object const& target, char const* key, object const& value);
static void del(object const&target, char const* key);
};
}}}
``
[endsect]
[section Class `attribute_policies` static functions]
``
static object const& set(object const& target, char const* key, object const& value);
``
[variablelist
[[Requires][key is an [link ntbs].]]
[[Effects][sets the attribute of target named by key to value.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
``
static void del(object const&target, char const* key);
``
[variablelist
[[Requires][key is an [link ntbs].]]
[[Effects][deletes the attribute of target named by key.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `const_objattribute_policies`]
The policies which are used for proxies representing an attribute access to a const object when the attribute name is given as a const object.
``
namespace boost { namespace python { namespace api
{
struct const_objattribute_policies
{
typedef object const& key_type;
static object get(object const& target, object const& key);
};
}}}
``
[endsect]
[section Class `const_objattribute_policies` static functions]
``
static object get(object const& target, object const& key);
``
[variablelist
[[Requires][key is an object holding a string.]]
[[Effects][accesses the attribute of target named by key.]]
[[Returns][An object managing the result of the attribute access.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `objattribute_policies`]
The policies which are used for proxies representing an attribute access to a mutable object when the attribute name is given as a const object.
``
namespace boost { namespace python { namespace api
{
struct objattribute_policies : const_objattribute_policies
{
static object const& set(object const& target, object const& key, object const& value);
static void del(object const&target, object const& key);
};
}}}
``
[endsect]
[section Class `objattribute_policies` static functions]
``
static object const& set(object const& target, object const& key, object const& value);
``
[variablelist
[[Requires][key is an object holding a string.]]
[[Effects][sets the attribute of target named by key to value.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
``
static void del(object const&target, object const& key);
``
[variablelist
[[Requires][key is an object holding a string.]]
[[Effects][deletes the attribute of target named by key.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `const_item_policies`]
The policies which are used for proxies representing an item access (via the Python bracket operators []) to a const object.
``
namespace boost { namespace python { namespace api
{
struct const_item_policies
{
typedef object key_type;
static object get(object const& target, object const& key);
};
}}}
``
[endsect]
[section Class `const_item_policies` static functions]
``
static object get(object const& target, object const& key);
``
[variablelist
[[Effects][accesses the item of target specified by key.]]
[[Returns][An object managing the result of the item access.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `item_policies`]
The policies which are used for proxies representing an item access (via the Python bracket operators []) to a mutable object.
``
namespace boost { namespace python { namespace api
{
struct item_policies : const_item_policies
{
static object const& set(object const& target, object const& key, object const& value);
static void del(object const& target, object const& key);
};
}}}
``
[endsect]
[section Class `item_policies` static functions]
``
static object const& set(object const& target, object const& key, object const& value);
``
[variablelist
[[Effects][sets the item of target specified by key to value.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
``
static void del(object const& target, object const& key);
``
[variablelist
[[Effects][deletes the item of target specified by key.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `const_slice_policies`]
The policies which are used for proxies representing an slice access (via the Python slice notation [x:y]) to a const object.
``
namespace boost { namespace python { namespace api
{
struct const_slice_policies
{
typedef std::pair<handle<>, handle<> > key_type;
static object get(object const& target, key_type const& key);
};
}}}
``
[endsect]
[section Class `const_slice_policies` static functions]
``
static object get(object const& target, key_type const& key);
``
[variablelist
[[Effects][accesses the slice of target specified by key.]]
[[Returns][An object managing the result of the slice access.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class `slice_policies`]
The policies which are used for proxies representing an slice access to a mutable object.
``
namespace boost { namespace python { namespace api
{
struct slice_policies : const_slice_policies
{
static object const& set(object const& target, key_type const& key, object const& value);
static void del(object const& target, key_type const& key);
};
}}}
``
[endsect]
[section Class `slice_policies` static functions]
``
static object const& set(object const& target, key_type const& key, object const& value);
``
[variablelist
[[Effects][sets the slice of target specified by key to value.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
``
static void del(object const& target, key_type const& key);
``
[variablelist
[[Effects][deletes the slice of target specified by key.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] if a Python exception is raised.]]
]
[endsect]
[section Class template `object_operators`]
This is the base class of object and its proxy template used to supply common interface: member functions, and operators which must be defined within the class body. Its template parameter U is expected to be a class derived from object_operators<U>. In practice users should never use this class directly, but it is documented here because it supplies important interface to object and its proxies.
``
namespace boost { namespace python { namespace api
{
template <class U>
class object_operators
{
public:
// function call
//
object operator()() const;
template <class A0>
object operator()(A0 const&) const;
template <class A0, class A1>
object operator()(A0 const&, A1 const&) const;
...
template <class A0, class A1,...class An>
object operator()(A0 const&, A1 const&,...An const&) const;
detail::args_proxy operator* () const;
object operator()(detail::args_proxy const &args) const;
object operator()(detail::args_proxy const &args,
detail::kwds_proxy const &kwds) const;
// truth value testing
//
typedef unspecified bool_type;
operator bool_type() const;
// Attribute access
//
proxy<const_object_attribute> attr(char const*) const;
proxy<object_attribute> attr(char const*);
proxy<const_object_objattribute> attr(object const&) const;
proxy<object_objattribute> attr(object const&);
// item access
//
template <class T>
proxy<const_object_item> operator[](T const& key) const;
template <class T>
proxy<object_item> operator[](T const& key);
// slicing
//
template <class T, class V>
proxy<const_object_slice> slice(T const& start, V const& end) const
template <class T, class V>
proxy<object_slice> slice(T const& start, V const& end);
};
}}}
``
[endsect]
[section Class template `object_operators` observer functions]
``
object operator()() const;
template <class A0>
object operator()(A0 const&) const;
template <class A0, class A1>
object operator()(A0 const&, A1 const&) const;
...
template <class A0, class A1,...class An>
object operator()(A0 const& a1, A1 const& a2,...An const& aN) const;
``
[variablelist
[[Effects][`call<object>(object(*static_cast<U*>(this)).ptr(), a1, a2,...aN)`]]
]
``object operator()(detail::args_proxy const &args) const; ``
[variablelist
[[Effects][`call object with arguments given by the tuple args`]]
]
``object operator()(detail::args_proxy const &args,
detail::kwds_proxy const &kwds) const;
``
[variablelist
[[Effects][`call object with arguments given by the tuple args, and named arguments given by the dictionary kwds`]]
]
``operator bool_type() const;``
[variablelist
[[Effects][Tests truth value of `*this`.]]
[[Returns][`call<object>(object(*static_cast<U*>(this)).ptr(), a1, a2,...aN)`]]
]
``
proxy<const_object_attribute> attr(char const* name) const;
proxy<object_attribute> attr(char const* name);
``
[variablelist
[[Requires][name is an [link ntbs].]]
[[Effects][accesses the named attribute of *this.]]
[[Returns][a proxy object which binds `object(*static_cast<U*>(this))` as its target, and name as its key.]]
]
``
proxy<const_object_objattribute> attr(const object& name) const;
proxy<object_objattribute> attr(const object& name);
``
[variablelist
[[Requires][name is a object holding a string.]]
[[Effects][accesses the named attribute of `*this`.]]
[[Returns][a proxy object which binds `object(*static_cast<U*>(this))` as its target, and name as its key.]]
]
``
template <class T>
proxy<const_object_item> operator[](T const& key) const;
template <class T>
proxy<object_item> operator[](T const& key);
``
[variablelist
[[Effects][accesses the item of `*this` indicated by key.]]
[[Returns][a proxy object which binds `object(*static_cast<U*>(this))` as its target, and object(key) as its key.]]
]
``
template <class T, class V>
proxy<const_object_slice> slice(T const& start; start, V const& finish) const
template <class T, class V>
proxy<object_slice> slice(T const& start; start, V const& finish);
``
[variablelist
[[Effects][accesses the slice of `*this` indicated by `std::make_pair(object(start), object(finish))`.]]
[[Returns][a proxy object which binds `object(*static_cast<U*>(this))` as its target, and `std::make_pair(object(start), object(finish))` as its key.]]
]
[endsect]
[section Class `object`]
The intention is that object acts as much like a Python variable as possible. Thus expressions you'd expect to work in Python should generally work in the same way from C++. Most of object's interface is provided by its base class `object_operators<object>`, and the free functions defined in this header.
``
namespace boost { namespace python { namespace api
{
class object : public object_operators<object>
{
public:
object();
object(object const&);
template <class T>
explicit object(T const& x);
~object();
object& operator=(object const&);
PyObject* ptr() const;
bool is_none() const;
};
}}}
``
[endsect]
[section Class `object` constructors and destructor]
``object();``
[variablelist
[[Effects][Constructs an object managing a reference to the Python None object.]]
[[Throws][nothing.]]
]
``template <class T>
explicit object(T const& x);
``
[variablelist
[[Effects][converts x to python and manages a reference to it.]]
[[Throws][[link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set] and sets a Python TypeError exception if no such conversion is possible.]]
]
``
~object();
``
[variablelist
[[Effects][decrements the reference count of the internally-held object.]]
]
[endsect]
[section Class `object` modifiers]
``PyObject* ptr() const;``
[variablelist
[[Returns] [a pointer to the internally-held Python object.]]
]
``bool is_none() const;``
[variablelist
[[Returns] [result of `(ptr() == Py_None)`]]
]
[endsect]
[section Class template `proxy`]
This template is instantiated with various Policies described in this document in order to implement attribute, item, and slice access for object. It stores an object of type Policies::key_type.
``
namespace boost { namespace python { namespace api
{
template <class Policies>
class proxy : public object_operators<proxy<Policies> >
{
public:
operator object() const;
proxy const& operator=(proxy const&) const;
template <class T>
inline proxy const& operator=(T const& rhs) const;
void del() const;
template <class R>
proxy operator+=(R const& rhs);
template <class R>
proxy operator-=(R const& rhs);
template <class R>
proxy operator*=(R const& rhs);
template <class R>
proxy operator/=(R const& rhs);
template <class R>
proxy operator%=(R const& rhs);
template <class R>
proxy operator<<=(R const& rhs);
template <class R>
proxy operator>>=(R const& rhs);
template <class R>
proxy operator&=(R const& rhs);
template <class R>
proxy operator|=(R const& rhs);
};
}}}
``
[endsect]
[section Class template `proxy` observer functions]
``operator object() const;``
[variablelist
[[Effects][applies `Policies::get(target, key)` with the proxy's target and key objects.]]
]
[endsect]
[section Class template `proxy` modifier functions]
``
proxy const& operator=(proxy const& rhs) const;
template <class T>
inline proxy const& operator=(T const& rhs) const;
``
[variablelist
[[Effects][ `Policies::set(target, key , object(rhs))` with the proxy's target and key objects.]]
]
``
template <class R>
proxy operator+=(R const& rhs);
template <class R>
proxy operator-=(R const& rhs);
template <class R>
proxy operator*=(R const& rhs);
template <class R>
proxy operator/=(R const& rhs);
template <class R>
proxy operator%=(R const& rhs);
template <class R>
proxy operator<<=(R const& rhs);
template <class R>
proxy operator>>=(R const& rhs);
template <class R>
proxy operator&=(R const& rhs);
template <class R>
proxy operator|=(R const& rhs);
``
[variablelist
[[Effects][for a given `operator@=`, `object(*this) @= rhs;`]]
[[Returns][`*this`]]
]
``void del() const;``
[variablelist
[[Effects][Policies::del(target, key ) with the proxy's target and key objects.]]
]
[endsect]
[section Functions]
``
template <class T>
void del(proxy<T> const& x);
``
[variablelist
[[Effects][`x.del()`]]
]
``
template<class L,class R> object operator>(L const&l,R const&r);
template<class L,class R> object operator>=(L const&l,R const&r);
template<class L,class R> object operator<(L const&l,R const&r);
template<class L,class R> object operator<=(L const&l,R const&r);
template<class L,class R> object operator==(L const&l,R const&r);
template<class L,class R> object operator!=(L const&l,R const&r);
``
[variablelist
[[Effects][returns the result of applying the operator to `object(l)` and `object(r)`, respectively, in Python.]]
]
``
template<class L,class R> object operator+(L const&l,R const&r);
template<class L,class R> object operator-(L const&l,R const&r);
template<class L,class R> object operator*(L const&l,R const&r);
template<class L,class R> object operator/(L const&l,R const&r);
template<class L,class R> object operator%(L const&l,R const&r);
template<class L,class R> object operator<<(L const&l,R const&r);
template<class L,class R> object operator>>(L const&l,R const&r);
template<class L,class R> object operator&(L const&l,R const&r);
template<class L,class R> object operator^(L const&l,R const&r);
template<class L,class R> object operator|(L const&l,R const&r);
``
[variablelist
[[Effects][returns the result of applying the operator to `object(l)` and `object(r)`, respectively, in Python.]]
]
``
template<class R> object& operator+=(object&l,R const&r);
template<class R> object& operator-=(object&l,R const&r);
template<class R> object& operator*=(object&l,R const&r);
template<class R> object& operator/=(object&l,R const&r);
template<class R> object& operator%=(object&l,R const&r);
template<class R> object& operator<<=(object&l,R const&r)
template<class R> object& operator>>=(object&l,R const&r);
template<class R> object& operator&=(object&l,R const&r);
template<class R> object& operator^=(object&l,R const&r);
template<class R> object& operator|=(object&l,R const&r);
``
[variablelist
[[Effects][assigns to `l` the result of applying the corresponding Python inplace operator to `l` and `object(r)`, respectively.]]
[[Returns][l]]
]
``long len(object const& obj);``
[variablelist
[[Effects][`PyObject_Length(obj.ptr())`]]
[[Returns][`len()` of object.]]
]
[endsect]
[section Example]
Python code:
``
def sum_items(seq):
result = 0
for x in seq:
result += x
return result
``
C++ version
``
object sum_items(object seq)
{
object result = object(0);
for (int i = 0; i < len(seq); ++i)
result += seq[i];
return result;
}
``
[endsect]
[endsect]

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@@ -0,0 +1,11 @@
[chapter Object Wrappers
[quickbook 1.7]
]
[include dict.qbk]
[include list.qbk]
[include long.qbk]
[include object.qbk]
[include str.qbk]
[include slice.qbk]
[include tuple.qbk]

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@@ -0,0 +1,31 @@
[section boost/python/opaque_pointer_converter.hpp]
[section Introduction]
`opaque<>` registers itself as a converter from Python objects to pointers to undefined types and vice versa.
``
namespace boost { namespace python
{
template<class Pointee>
struct opaque
{
opaque();
};
}}
``
[endsect]
[section Class template `opaque` constructor]
``opaque();``
[variablelist
[[Effects][
* Registers the instance as a [link to_from_python_type_conversion.boost_python_lvalue_from_pytype_.class_template_lvalue_from_pytyp `lvalue_from_pytype`] converter from Python objects into opaque pointers.
The Python Objects created are named after the type pointed to by the opaque pointer being wrapped.
* Registers the instance as a [link to_from_python_type_conversion.boost_python_to_python_converter.class_template_to_python_convert `to_python_converter`] from opaque pointers to Python objects.
]]
]
[note If there is already an instance registered by another module, this instance doesn't try to register again in order to avoid warnings about multiple registrations.]
[endsect]
[section Macro `BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(Pointee)`]
This macro must be used to define specializations of the [link utility_and_infrastructure.boost_python_type_id_hpp.functions `type_id`] function which can't be instantiated for incomplete types.
[note The macro must be invoked in every translation unit which uses the opaque converter.]
[endsect]
[endsect]

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[section boost/python/operators.hpp]
[section Introduction]
<boost/python/operators.hpp> provides types and functions for automatically generating Python [@http://www.python.org/doc/ref/specialnames.html special methods] from the corresponding C++ constructs. Most of these constructs are operator expressions, hence the name. To use the facility, substitute the [link high_level_components.boost_python_operators_hpp.object_self self] object for an object of the class type being wrapped in the expression to be exposed, and pass the result to [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu class_<>::def()]. Much of what is exposed in this header should be considered part of the implementation, so is not documented in detail here.
[endsect]
[section Class `self_ns::self_t`]
`self_ns::self_t` is the actual type of the [link high_level_components.boost_python_operators_hpp.object_self self] object. The library isolates `self_t` in its own namespace, `self_ns`, in order to prevent the generalized operator templates which operate on it from being found by argument-dependent lookup in other contexts. This should be considered an implementation detail, since users should never have to mention `self_t` directly.
``
namespace boost { namespace python { namespace self_ns {
{
unspecified-type-declaration self_t;
// inplace operators
template <class T> operator_<unspecified> operator+=(self_t, T);
template <class T> operator_<unspecified> operator-=(self_t, T);
template <class T> operator_<unspecified> operator*=(self_t, T);
template <class T> operator_<unspecified> operator/=(self_t, T);
template <class T> operator_<unspecified> operator%=(self_t, T);
template <class T> operator_<unspecified> operator>>=(self_t, T);
template <class T> operator_<unspecified> operator<<=(self_t, T);
template <class T> operator_<unspecified> operator&=(self_t, T);
template <class T> operator_<unspecified> operator^=(self_t, T);
template <class T> operator_<unspecified> operator|=(self_t, T);
// comparisons
template <class L, class R> operator_<unspecified> operator==(L const&, R const&);
template <class L, class R> operator_<unspecified> operator!=(L const&, R const&);
template <class L, class R> operator_<unspecified> operator<(L const&, R const&);
template <class L, class R> operator_<unspecified> operator>(L const&, R const&);
template <class L, class R> operator_<unspecified> operator<=(L const&, R const&);
template <class L, class R> operator_<unspecified> operator>=(L const&, R const&);
// non-member operations
template <class L, class R> operator_<unspecified> operator+(L const&, R const&);
template <class L, class R> operator_<unspecified> operator-(L const&, R const&);
template <class L, class R> operator_<unspecified> operator*(L const&, R const&);
template <class L, class R> operator_<unspecified> operator/(L const&, R const&);
template <class L, class R> operator_<unspecified> operator%(L const&, R const&);
template <class L, class R> operator_<unspecified> operator>>(L const&, R const&);
template <class L, class R> operator_<unspecified> operator<<(L const&, R const&);
template <class L, class R> operator_<unspecified> operator&(L const&, R const&);
template <class L, class R> operator_<unspecified> operator^(L const&, R const&);
template <class L, class R> operator_<unspecified> operator|(L const&, R const&);
template <class L, class R> operator_<unspecified> pow(L const&, R const&);
// unary operations
operator_<unspecified> operator-(self_t);
operator_<unspecified> operator+(self_t);
operator_<unspecified> operator~(self_t);
operator_<unspecified> operator!(self_t);
// value operations
operator_<unspecified> int_(self_t);
operator_<unspecified> long_(self_t);
operator_<unspecified> float_(self_t);
operator_<unspecified> complex_(self_t);
operator_<unspecified> str(self_t);
operator_<unspecified> repr(self_t);
}}};
``
The tables below describe the methods generated when the results of the expressions described are passed as arguments to [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu class_<>::def()]. `x` is an object of the class type being wrapped.
[section `self_t` inplace operators]
In the table below, If `r` is an object of type [link high_level_components.boost_python_operators_hpp.class_template_other other<T>], `y` is an object of type `T`; otherwise, `y` is an object of the same type as `r`.
[table
[[C++ Expression][Python Method Name][C++ Implementation]]
[[`self += r`][`__iadd__`][`x += y`]]
[[`self -= r`][`__isub__`][`x -= y`]]
[[`self *= r`][`__imul__`][`x *= y`]]
[[`self /= r`][`__idiv__`][`x /= y`]]
[[`self %= r`][`__imod__`][`x %= y`]]
[[`self >>= r`][`__irshift__`][`x >>= y`]]
[[`self <<= r`][`__ilshift__`][`x <<= y`]]
[[`self &= r`][`__iand__`][`x &= y`]]
[[`self ^= r`][`__ixor__`][`x ^= y`]]
[[`self |= r`][`__ior__`][`x |= y`]]
]
[endsect]
[section `self_t` comparison functions]
In the tables below, if `r` is of type [link high_level_components.boost_python_operators_hpp.class_self_ns_self_t self_t], `y` is an object of the same type as `x`;
if `l` or `r` is an object of type [link high_level_components.boost_python_operators_hpp.class_template_other other<T>], `y` is an object of type `T`;
otherwise, `y` is an object of the same type as `l` or `r`.
`l` is never of type [link high_level_components.boost_python_operators_hpp.class_self_ns_self_t self_t].
The column of Python Expressions illustrates the expressions that will be supported in Python for objects convertible to the types of x and y. The secondary operation arises due to Python's [@http://www.python.org/doc/ref/customization.html#l2h-89 reflection rules] for rich comparison operators, and are only used when the corresponding operation is not defined as a method of the y object.
[table
[[C++ Expression][Python Method Name][C++ Implementation][Python Expression (primary, secondary)]]
[[`self == r`][`__eq__`][`x == y`][`x == y`, `y == x`]]
[[`l == self`][`__eq__`][`y == x`][`y == x`, `x == y`]]
[[`self != r`][`__nq__`][`x != y`][`x != y`, `y != x`]]
[[`l != self`][`__nq__`][`y != x`][`y != x`, `x != y`]]
[[`self < r`][`__lt__`][`x < y`][`x < y`, `y > x`]]
[[`l < self`][`__gt__`][`y < x`][`y > x`, `x < y`]]
[[`self > r`][`__gt__`][`x > y`][`x > y`, `y < x`]]
[[`l > self`][`__lt__`][`y > x`][`y < x`, `x > y`]]
[[`self <= r`][`__le__`][`x <= y`][`x <= y`, `y >= x`]]
[[`l <= self`][`__ge__`][`y <= x`][`y >= x`, `x <= y`]]
[[`self >= r`][`__ge__`][`x >= y`][`x >= y`, `y <= x`]]
[[`l <= self`][`__le__`][`y >= x`][`y <= x`, `x >= y`]]
]
[endsect]
[section `self_t` non-member operations]
The operations whose names begin with "__r" below will only be called if the left-hand operand does not already support the given operation, as described [@http://www.python.org/doc/current/ref/numeric-types.html#l2h-152 here].
[table
[[C++ Expression][Python Method Name][C++ Implementation]]
[[`self + r`][`__add__`][`x + y`]]
[[`l + self`][`__radd__`][`y + x`]]
[[`self - r`][`__sub__`][`x - y`]]
[[`l - self`][`__rsub__`][`y - x`]]
[[`self * r`][`__mult__`][`x * y`]]
[[`l * self`][`__rmult__`][`y * x`]]
[[`self / r`][`__div__`][`x / y`]]
[[`l / self`][`__rdiv__`][`y / x`]]
[[`self % r`][`__mod__`][`x % y`]]
[[`l % self`][`__rmod__`][`y % x`]]
[[`self >> r`][`__rshift__`][`x >> y`]]
[[`l >> self`][`__rrshift__`][`y >> x`]]
[[`self << r`][`__lshift__`][`x << y`]]
[[`l << self`][`__rlshift__`][`y << x`]]
[[`self & r`][`__and__`][`x & y`]]
[[`l & self`][`__rand__`][`y & x`]]
[[`self ^ r`][`__xor__`][`x ^ y`]]
[[`l ^ self`][`__rxor__`][`y ^ x`]]
[[`self | r`][`__or__`][`x | y`]]
[[`l | self`][`__ror__`][`y | x`]]
[[`pow(self, r)`][`__pow__`][`x ** y`]]
[[`pow(l, self)`][`__rpow__`][`y ** x`]]
]
[endsect]
[section `self_t` unary operations]
[table
[[C++ Expression][Python Method Name][C++ Implementation]]
[[`-self`][`__neg__`][`-x`]]
[[`+self`][`__pos__`][`+x`]]
[[`~self`][`__invert__`][`~x`]]
[[`not self` or `!self`][`__nonzero__`][`!!x`]]
]
[endsect]
[section `self_t` value operations]
[table
[[C++ Expression][Python Method Name][C++ Implementation]]
[[`int_(self)`][`__int__`][`long(x)`]]
[[`long_(self)`][`__long__`][`PyLong_FromLong(x)`]]
[[`float_(self)`][`__float__`][`double(x)`]]
[[`complex_(self)`][`__complex__`][`std::complex<double>(x)`]]
[[`str(self)`][`__str__`][`lexical_cast<std::string>(x)`]]
[[`repr(self)`][`__repr__`][`lexical_cast<std::string>(x)`]]
]
[endsect]
[endsect]
[section Class template `other`]
Instances of `other<T>` can be used in operator expressions with [link high_level_components.boost_python_operators_hpp.object_self self]; the result is equivalent to the same expression with a `T` object in place of `other<T>`. Use `other<T>` to prevent construction of a `T` object in case it is heavyweight, when no constructor is available, or simply for clarity.
``
namespace boost { namespace python
{
template <class T>
struct other
{
};
}}
``
[endsect]
[section Class template `detail::operator_`]
Instantiations of `detail::operator_<>` are used as the return type of operator expressions involving [link high_level_components.boost_python_operators_hpp.object_self self]. This should be considered an implementation detail and is only documented here as a way of showing how the result of self-expressions match calls to [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu `class_<>::def()`].
``
namespace boost { namespace python { namespace detail
{
template <unspecified>
struct operator_
{
};
}}}
``
[endsect]
[section Object `self`]
``
namespace boost { namespace python
{
using self_ns::self;
}}
``
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/operators.hpp>
#include <boost/operators.hpp>
struct number
: boost::integer_arithmetic<number>
{
explicit number(long x_) : x(x_) {}
operator long() const { return x; }
template <class T>
number& operator+=(T const& rhs)
{ x += rhs; return *this; }
template <class T>
number& operator-=(T const& rhs)
{ x -= rhs; return *this; }
template <class T>
number& operator*=(T const& rhs)
{ x *= rhs; return *this; }
template <class T>
number& operator/=(T const& rhs)
{ x /= rhs; return *this; }
template <class T>
number& operator%=(T const& rhs)
{ x %= rhs; return *this; }
long x;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(demo)
{
class_<number>("number", init<long>())
// interoperate with self
.def(self += self)
.def(self + self)
.def(self -= self)
.def(self - self)
.def(self *= self)
.def(self * self)
.def(self /= self)
.def(self / self)
.def(self %= self)
.def(self % self)
// Convert to Python int
.def(int_(self))
// interoperate with long
.def(self += long())
.def(self + long())
.def(long() + self)
.def(self -= long())
.def(self - long())
.def(long() - self)
.def(self *= long())
.def(self * long())
.def(long() * self)
.def(self /= long())
.def(self / long())
.def(long() / self)
.def(self %= long())
.def(self % long())
.def(long() % self)
;
}
``
[endsect]
[endsect]

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[section boost/python/overloads.hpp]
[section Introduction]
Defines facilities for generating families of overloaded Python functions and extension class methods from C++ functions and member functions with default arguments, or from similar families of C++ overloads
[section overload-dispatch-expressions]
An overload-dispatch-expression is used to describe a family of overloaded methods to be generated for an extension class. It has the following properties:
[variablelist
[[docstring][An [link ntbs] whose value will bound to the methods' `__doc__` attribute]]
[[keywords][A [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] which will be used to name (a trailing subsequence of) the arguments to the generated methods.]]
[[call policies][An instance of some type which models CallPolicies.]]
[[minimum arity][The minimum number of arguments to be accepted by a generated method overload.]]
[[maximum arity][The maximum number of arguments to be accepted by a generated method overload.]]
]
[endsect]
[endsect]
[section OverloadDispatcher Concept]
An OverloadDispatcher X is a class which has a minimum arity and a maximum arity, and for which the following following are valid overload-dispatch-expressions, with the same minimum and maximum arity as the OverloadDispatcher.
``
X()
X(docstring)
X(docstring, keywords)
X(keywords, docstring)
X()[policies]
X(docstring)[policies]
X(docstring, keywords)[policies]
X(keywords, docstring)[policies]
``
* If policies are supplied, it must be an instance of a type which models [link concepts.callpolicies CallPolicies], and will be used as the result's call policies. Otherwise the result's call policies will be an instance of [link function_invocation_and_creation.models_of_callpolicies.boost_python_default_call_polici `default_call_policies`].
* If docstring is supplied it must be an [link ntbs], and will be used as the result's docstring. Otherwise the result has an empty docstring.
* If keywords is supplied it must be the result of a [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] whose length is no greater than X's maximum arity, and will be used as the result's keywords. Otherwise the result's keywords will be empty.
[endsect]
[section Macros]
``
BOOST_PYTHON_FUNCTION_OVERLOADS(name, func_id, min_args, max_args)
``
Expands to the definition of an OverloadDispatcher called name in the current scope which can be used to generate the following function invocation:
``func_id(a1, a2,...ai);``
for all `min_args <= i <= max_args`.
``
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(name, member_name, min_args, max_args)
``
Expands to the definition of an OverloadDispatcher called name in the current scope which can be used to generate the following function invocation:
``x.member_name(a1, a2,...ai);``
for all min_args <= i <= max_args, where x is a reference to an object of class type.
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/args.hpp>
#include <boost/python/tuple.hpp>
#include <boost/python/class.hpp>
#include <boost/python/overloads.hpp>
#include <boost/python/return_internal_reference.hpp>
using namespace boost::python;
tuple f(int x = 1, double y = 4.25, char const* z = "wow")
{
return make_tuple(x, y, z);
}
BOOST_PYTHON_FUNCTION_OVERLOADS(f_overloads, f, 0, 3)
struct Y {};
struct X
{
Y& f(int x, double y = 4.25, char const* z = "wow")
{
return inner;
}
Y inner;
};
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(f_member_overloads, f, 1, 3)
BOOST_PYTHON_MODULE(args_ext)
{
def("f", f,
f_overloads(
args("x", "y", "z"), "This is f's docstring"
));
class_<Y>("Y")
;
class_<X>("X", "This is X's docstring")
.def("f1", &X::f,
f_member_overloads(
args("x", "y", "z"), "f's docstring"
)[return_internal_reference<>()]
)
;
}
``
[endsect]
[endsect]

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[section Pickle support]
[section Introduction]
Pickle is a Python module for object serialization, also known as persistence, marshalling, or flattening.
It is often necessary to save and restore the contents of an object to a file. One approach to this problem is to write a pair of functions that read and write data from a file in a special format. A powerful alternative approach is to use Python's pickle module. Exploiting Python's ability for introspection, the pickle module recursively converts nearly arbitrary Python objects into a stream of bytes that can be written to a file.
The Boost Python Library supports the pickle module through the interface as described in detail in the [@https://docs.python.org/2/library/pickle.html Python Library Reference for pickle]. This interface involves the special methods `__getinitargs__`, `__getstate__` and `__setstate__` as described in the following. Note that `Boost.Python` is also fully compatible with Python's cPickle module.
[endsect]
[section The Pickle Interface]
At the user level, the Boost.Python pickle interface involves three special methods:
[variablelist
[[__getinitargs__][When an instance of a Boost.Python extension class is pickled, the pickler tests if the instance has a `__getinitargs__` method. This method must return a Python `tuple` (it is most convenient to use a [link object_wrappers.boost_python_tuple_hpp.class_tuple `boost::python::tuple`]). When the instance is restored by the unpickler, the contents of this tuple are used as the arguments for the class constructor.
If `__getinitargs__` is not defined, `pickle.load` will call the constructor (`__init__`) without arguments; i.e., the object must be default-constructible.]]
[[__getstate__][When an instance of a `Boost.Python` extension class is pickled, the pickler tests if the instance has a `__getstate__` method. This method should return a Python object representing the state of the instance.]]
[[__setstate__][When an instance of a `Boost.Python` extension class is restored by the unpickler (`pickle.load`), it is first constructed using the result of `__getinitargs__` as arguments (see above). Subsequently the unpickler tests if the new instance has a `__setstate__` method. If so, this method is called with the result of `__getstate__` (a Python object) as the argument.]]
]
The three special methods described above may be `.def()`\ 'ed individually by the user. However, `Boost.Python` provides an easy to use high-level interface via the `boost::python::pickle_suite` class that also enforces consistency: `__getstate__` and `__setstate__` must be defined as pairs. Use of this interface is demonstrated by the following examples.
[endsect]
[section Example]
There are three files in `python/test` that show how to provide pickle support.
[section pickle1.cpp]
The C++ class in this example can be fully restored by passing the appropriate argument to the constructor. Therefore it is sufficient to define the pickle interface method `__getinitargs__`. This is done in the following way:
Definition of the C++ pickle function:
``
struct world_pickle_suite : boost::python::pickle_suite
{
static
boost::python::tuple
getinitargs(world const& w)
{
return boost::python::make_tuple(w.get_country());
}
};
``
Establishing the Python binding:
``
class_<world>("world", args<const std::string&>())
// ...
.def_pickle(world_pickle_suite())
// ...
``
[endsect]
[section pickle2.cpp]
The C++ class in this example contains member data that cannot be restored by any of the constructors. Therefore it is necessary to provide the `__getstate__`/`__setstate__` pair of pickle interface methods:
Definition of the C++ pickle functions:
``
struct world_pickle_suite : boost::python::pickle_suite
{
static
boost::python::tuple
getinitargs(const world& w)
{
// ...
}
static
boost::python::tuple
getstate(const world& w)
{
// ...
}
static
void
setstate(world& w, boost::python::tuple state)
{
// ...
}
};
``
Establishing the Python bindings for the entire suite:
``
class_<world>("world", args<const std::string&>())
// ...
.def_pickle(world_pickle_suite())
// ...
``
For simplicity, the `__dict__` is not included in the result of `__getstate__`. This is not generally recommended, but a valid approach if it is anticipated that the object's `__dict__` will always be empty. Note that the safety guard described below will catch the cases where this assumption is violated.
[endsect]
[section pickle3.cpp]
This example is similar to pickle2.cpp. However, the object's `__dict__` is included in the result of `__getstate__`. This requires a little more code but is unavoidable if the object's `__dict__` is not always empty.
[endsect]
[endsect]
[section Pitfall and Safety Guard]
The pickle protocol described above has an important pitfall that the end user of a Boost.Python extension module might not be aware of:
[*`__getstate__` is defined and the instance's `__dict__` is not empty.]
The author of a `Boost.Python` extension class might provide a `__getstate__` method without considering the possibilities that:
* his class is used in Python as a base class. Most likely the `__dict__` of instances of the derived class needs to be pickled in order to restore the instances correctly.
* the user adds items to the instance's `__dict__` directly. Again, the `__dict__` of the instance then needs to be pickled.
To alert the user to this highly unobvious problem, a safety guard is provided. If `__getstate__` is defined and the instance's `__dict__` is not empty, `Boost.Python` tests if the class has an attribute `__getstate_manages_dict__`. An exception is raised if this attribute is not defined:
``
RuntimeError: Incomplete pickle support (__getstate_manages_dict__ not set)
``
To resolve this problem, it should first be established that the `__getstate__` and `__setstate__` methods manage the instances's `__dict__` correctly. Note that this can be done either at the C++ or the Python level. Finally, the safety guard should intentionally be overridden. E.g. in C++ (from pickle3.cpp):
``
struct world_pickle_suite : boost::python::pickle_suite
{
// ...
static bool getstate_manages_dict() { return true; }
};
``
Alternatively in Python:
``
import your_bpl_module
class your_class(your_bpl_module.your_class):
__getstate_manages_dict__ = 1
def __getstate__(self):
# your code here
def __setstate__(self, state):
# your code here
``
[endsect]
[section Practical Advice]
* In `Boost.Python` extension modules with many extension classes, providing complete pickle support for all classes would be a significant overhead. In general complete pickle support should only be implemented for extension classes that will eventually be pickled.
* Avoid using `__getstate__` if the instance can also be reconstructed by way of `__getinitargs__`. This automatically avoids the pitfall described above.
* If `__getstate__` is required, include the instance's `__dict__` in the Python object that is returned.
[endsect]
[section Light-weight alternative: pickle support implemented in Python]
The pickle4.cpp example demonstrates an alternative technique for implementing pickle support. First we direct Boost.Python via the class_::enable_pickling() member function to define only the basic attributes required for pickling:
``
class_<world>("world", args<const std::string&>())
// ...
.enable_pickling()
// ...
``
This enables the standard Python pickle interface as described in the Python documentation. By "injecting" a `__getinitargs__` method into the definition of the wrapped class we make all instances pickleable:
``
# import the wrapped world class
from pickle4_ext import world
# definition of __getinitargs__
def world_getinitargs(self):
return (self.get_country(),)
# now inject __getinitargs__ (Python is a dynamic language!)
world.__getinitargs__ = world_getinitargs
``
See also the tutorial section on injecting additional methods from Python.
[endsect]
[endsect]

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[section boost/python/pointee.hpp]
[section Introduction]
<boost/python/pointee.hpp> introduces a traits metafunction `template pointee<T>` that can be used to extract the "pointed-to" type from the type of a pointer or smart pointer.
[endsect]
[section Class template `pointee`]
`pointee<T>` is used by the [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel `class_<...>`] template to deduce the type being held when a pointer or smart pointer type is used as its HeldType argument.
``
namespace boost { namespace python
{
template <class T> struct pointee
{
typedef T::element_type type;
};
// specialization for pointers
template <T> struct pointee<T*>
{
typedef T type;
};
}
``
[endsect]
[section Examples]
Given a 3rd-party smart pointer type `smart_pointer<T>`, one might partially specialize `pointee<smart_pointer<T> >` so that it can be used as the HeldType for a class wrapper:
``
#include <boost/python/pointee.hpp>
#include <boost/python/class.hpp>
#include <third_party_lib.hpp>
namespace boost { namespace python
{
template <class T> struct pointee<smart_pointer<T> >
{
typedef T type;
};
}}
BOOST_PYTHON_MODULE(pointee_demo)
{
class_<third_party_class, smart_pointer<third_party_class> >("third_party_class")
.def(...)
...
;
}
``
[endsect]
[endsect]

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[section boost/python/ptr.hpp]
[section Introduction]
<boost/python/ptr.hpp> defines the ptr() function template, which allows users to specify how to convert C++ pointer values to python in the context of implementing overridable virtual functions, invoking Python callable objects, or explicitly converting C++ objects to Python. Normally, when passing pointers to Python callbacks, the pointee is copied to ensure that the Python object never holds a dangling reference. To specify that the new Python object should merely contain a copy of a pointer p, the user can pass ptr(p) instead of passing p directly. This interface is meant to mirror the use of boost::ref(), which can be similarly used to prevent copying of referents.
ptr(p) returns an instance of [link function_invocation_and_creation.boost_python_ptr_hpp.class_template_pointer_wrapper `pointer_wrapper<>`], which can be detected using the [link function_invocation_and_creation.boost_python_ptr_hpp.metafunctions.class_template_is_pointer_wrappe `is_pointer_wrapper<>`] metafunction; [link function_invocation_and_creation.boost_python_ptr_hpp.metafunctions.class_template_unwrap_pointer `unwrap_pointer<>`] is a metafunction which extracts the original pointer type from a `pointer_wrapper<>`. These classes can be thought of as implementation details.
[endsect]
[section Functions]
``
template <class T>
pointer_wrapper<T> ptr(T x);
``
[variablelist
[[Requires][T is a pointer type.]]
[[Returns][pointer_wrapper<T>(x)]]
[[Throws][nothing.]]
]
[endsect]
[section Class template `pointer_wrapper`]
A "type envelope" which is returned by `ptr()`, used to indicate reference semantics for pointers passed to Python callbacks.
``
namespace boost { namespace python
{
template<class Ptr> class pointer_wrapper
{
public:
typedef Ptr type;
explicit pointer_wrapper(Ptr x);
operator Ptr() const;
Ptr get() const;
};
}}
``
[endsect]
[section Class template `pointer_wrapper` types]
``
typedef Ptr type;
``
The type of the pointer being wrapped.
[endsect]
[section Class template `pointer_wrapper` constructors and destructor]
``
explicit pointer_wrapper(Ptr x);
``
[variablelist
[[Requires][`Ptr` is a pointer type]]
[[Effects][Stores `x` in a the `pointer_wrapper<>`. ]]
[[Throws][nothing.]]
]
[endsect]
[section Class template `pointer_wrapper` observer functions]
``
operator Ptr() const;
Ptr get() const;
``
[variablelist
[[Returns][a copy of the stored pointer. ]]
[[Rationale][pointer_wrapper is intended to be a stand-in for the actual pointer type, but sometimes it's better to have an explicit way to retrieve the pointer. ]]
]
[endsect]
[section Metafunctions]
[section Class template `is_pointer_wrapper`]
A unary metafunction whose value is true iff its argument is a pointer_wrapper<>.
``
namespace boost { namespace python
{
template<class T> class is_pointer_wrapper
{
static unspecified value = ...;
};
}}
``
[variablelist
[[Returns][`true` iff `T` is a specialization of `pointer_wrapper<>`.
value is an integral constant convertible to bool of unspecified type ]]
]
[endsect]
[section Class template `unwrap_pointer`]
A unary metafunction which extracts the wrapped pointer type from a specialization of pointer_wrapper<>.
``
namespace boost { namespace python
{
template<class T> class unwrap_pointer
{
typedef unspecified type;
};
}}
``
[variablelist
[[Returns][`T::type` if `T` is a specialization of `pointer_wrapper<>`, `T` otherwise ]]
]
[endsect]
[endsect]
[section Example]
This example illustrates the use of ptr() to prevent an object from being copied:
``
#include <boost/python/call.hpp>
#include <boost/python/ptr.hpp>
class expensive_to_copy
{
...
};
void pass_as_arg(expensive_to_copy* x, PyObject* f)
{
// call the Python function f, passing a Python object built around
// which refers to *x by-pointer.
//
// *** Note: ensuring that *x outlives the argument to f() is ***
// *** up to the user! Failure to do so could result in a crash! ***
boost::python::call<void>(f, ptr(x));
}
...
``
[endsect]
[endsect]

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[section boost/python/pytype_function.hpp]
[section Introduction]
To support Pythonic signatures the converters should supply a `get_pytype` function returning a pointer to the associated `PyTypeObject`. See for example [link concepts.resultconverter `ResultConverter`] or [link to_from_python_type_conversion.boost_python_to_python_converter.class_template_to_python_convert.class_template_to_python_convert `to_python_converter`]. The classes in this header file are meant to be used when implmenting `get_pytype`. There are also `_direct` versions of the templates of `class T` which should be used with undecorated type parameter, expected to be in the conversion registry when the module loads.
[endsect]
[section Class `wrap_pytype`]
This template generates a static `get_pytype` member returning the template parameter.
``
namespace boost { namespace python { namespace converter{
template < PyTypeObject const *pytype >
class wrap_pytype
{
public:
static PyTypeObject const *get_pytype(){return pytype; }
};
}}}
``
[endsect]
[section Class `registered_pytype`]
This template should be used with template parameters which are (possibly decorated) types exported to python using [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel `class_`]. The generated a static `get_pytype` member returns the corresponding python type.
``
namespace boost { namespace python { namespace converter{
template < class T >
class registered_pytype
{
public:
static PyTypeObject const *get_pytype();
};
}}}
``
[endsect]
[section Class `expected_from_python_type`]
This template generates a static `get_pytype` member which inspects the registered `from_python` converters for the type `T` and returns a matching python type.
``
namespace boost { namespace python { namespace converter{
template < class T >
class expected_from_python_type
{
public:
static PyTypeObject const *get_pytype();
};
}}}
``
[endsect]
[section Class `to_python_target_type`]
This template generates a static `get_pytype` member returning the python type to which `T` can be converted.
``
namespace boost { namespace python { namespace converter{
template < class T >
class to_python_target_type
{
public:
static PyTypeObject const *get_pytype();
};
}}}
``
[endsect]
[section Example]
This example presumes that someone has implemented the standard noddy example module from the Python documentation, and placed the corresponding declarations in "noddy.h". Because `noddy_NoddyObject` is the ultimate trivial extension type, the example is a bit contrived: it wraps a function for which all information is contained in the type of its return value.
C++ module definition:
``
#include <boost/python/reference.hpp>
#include <boost/python/module.hpp>
#include "noddy.h"
struct tag {};
tag make_tag() { return tag(); }
using namespace boost::python;
struct tag_to_noddy
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //unnecessary overhead if py signatures are not supported
: wrap_pytype<&noddy_NoddyType> //inherits get_pytype from wrap_pytype
#endif
{
static PyObject* convert(tag const& x)
{
return PyObject_New(noddy_NoddyObject, &noddy_NoddyType);
}
};
BOOST_PYTHON_MODULE(to_python_converter)
{
def("make_tag", make_tag);
to_python_converter<tag, tag_to_noddy
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
, true
#endif
>(); //"true" because tag_to_noddy has member get_pytype
}
``
The following example registers to and from python converters using the templates expected_from_python_type and to_pyhton_target_type.
``
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/extract.hpp>
#include <boost/python/to_python_converter.hpp>
#include <boost/python/class.hpp>
using namespace boost::python;
struct A
{
};
struct B
{
A a;
B(const A& a_):a(a_){}
};
// Converter from A to python int
struct BToPython
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //unnecessary overhead if py signatures are not supported
: converter::to_python_target_type<A> //inherits get_pytype
#endif
{
static PyObject* convert(const B& b)
{
return incref(object(b.a).ptr());
}
};
// Conversion from python int to A
struct BFromPython
{
BFromPython()
{
boost::python::converter::registry::push_back
( &convertible
, &construct
, type_id< B >()
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
, &converter::expected_from_python_type<A>::get_pytype//convertible to A can be converted to B
#endif
);
}
static void* convertible(PyObject* obj_ptr)
{
extract<const A&> ex(obj_ptr);
if (!ex.check()) return 0;
return obj_ptr;
}
static void construct(
PyObject* obj_ptr,
converter::rvalue_from_python_stage1_data* data)
{
void* storage = (
(converter::rvalue_from_python_storage< B >*)data)-> storage.bytes;
extract<const A&> ex(obj_ptr);
new (storage) B(ex());
data->convertible = storage;
}
};
B func(const B& b) { return b ; }
BOOST_PYTHON_MODULE(pytype_function_ext)
{
to_python_converter< B , BToPython
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
,true
#endif
>(); //has get_pytype
BFromPython();
class_<A>("A") ;
def("func", &func);
}
>>> from pytype_function_ext import *
>>> print func.__doc__
func( (A)arg1) -> A :
C++ signature:
struct B func(struct B)
``
[endsect]
[endsect]

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[section boost/python/raw_function.hpp]
[section Introduction]
`raw_function(...)` is used to convert a function taking a [link object_wrappers.boost_python_tuple_hpp.class_tuple `tuple`] and a [link object_wrappers.boost_python_dict_hpp.class_dict `dict`] into a Python callable object which accepts a variable number of arguments and arbitrary keyword arguments.
[endsect]
[section Function `raw_function`]
``
template <class F>
object raw_function(F f, std::size_t min_args = 0);
``
[variablelist
[[Requires][f(tuple(), dict()) is well-formed.]]
[[Returns][a callable object which requires at least min_args arguments. When called, the actual non-keyword arguments will be passed in a tuple as the first argument to f, and the keyword arguments will be passed in a dict as the second argument to f. ]]
]
[endsect]
[section Example]
C++:
``
#include <boost/python/def.hpp>
#include <boost/python/tuple.hpp>
#include <boost/python/dict.hpp>
#include <boost/python/module.hpp>
#include <boost/python/raw_function.hpp>
using namespace boost::python;
tuple raw(tuple args, dict kw)
{
return make_tuple(args, kw);
}
BOOST_PYTHON_MODULE(raw_test)
{
def("raw", raw_function(raw));
}
``
Python:
``
>>> from raw_test import *
>>> raw(3, 4, foo = 'bar', baz = 42)
((3, 4), {'foo': 'bar', 'baz': 42})
``
[endsect]
[endsect]

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[section boost/python/reference_existing_object.hpp]
[section Class `reference_existing_object`]
`reference_existing_object` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions which return a reference or pointer to a C++ object. When the wrapped function is called, the value referenced by its return value is not copied. A new Python object is created which contains a pointer to the referent, and no attempt is made to ensure that the lifetime of the referent is at least as long as that of the corresponding Python object. Thus, it can be *highly dangerous* to use `reference_existing_object` without additional lifetime management from such models of [link concepts.callpolicies CallPolicies] as [link function_invocation_and_creation.models_of_callpolicies.boost_python_with_custodian_and_.class_with_custodian_and_ward `with_custodian_and_ward`]. This class is used in the implementation of [link function_invocation_and_creation.models_of_callpolicies.boost_python_return_internal_ref.class_template_return_internal_r `return_internal_reference`].
``
namespace boost { namespace python
{
struct reference_existing_object
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `reference_existing_object` metafunctions]
``template <class T> struct apply``
[variablelist
[[Requires][`T` is `U&` or `U*` for some `U`.]]
[[Returns][`typedef to_python_indirect<T, V> type;`, where V is a class whose static execute function constructs an instance holder containing an unowned `U*` pointing to the referent of the wrapped function's return value.]]
]
[endsect]
[section Example]
In C++:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/reference_existing_object.hpp>
#include <boost/python/return_value_policy.hpp>
#include <utility>
// classes to wrap
struct Singleton
{
Singleton() : x(0) {}
int exchange(int n) // set x and return the old value
{
std::swap(n, x);
return n;
}
int x;
};
Singleton& get_it()
{
static Singleton just_one;
return just_one;
}
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(singleton)
{
def("get_it", get_it,
return_value_policy<reference_existing_object>());
class_<Singleton>("Singleton")
.def("exchange", &Singleton::exchange)
;
}
``
Python code:
``
>>> import singleton
>>> s1 = singleton.get_it()
>>> s2 = singleton.get_it()
>>> id(s1) == id(s2) # s1 and s2 are not the same object
0
>>> s1.exchange(42) # but they reference the same C++ Singleton
0
>>> s2.exchange(99)
42
``
[endsect]
[endsect]

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[section boost/python/register_ptr_to_python.hpp]
[section Introduction]
<boost/python/register_ptr_to_python.hpp> supplies `register_ptr_to_python`, a function template which registers a conversion for smart pointers to Python. The resulting Python object holds a copy of the converted smart pointer, but behaves as though it were a wrapped copy of the pointee. If the pointee type has virtual functions and the class representing its dynamic (most-derived) type has been wrapped, the Python object will be an instance of the wrapper for the most-derived type. More than one smart pointer type for a pointee's class can be registered.
Note that in order to convert a Python `X` object to a `smart_ptr<X>&` (non-const reference), the embedded C++ object must be held by `smart_ptr<X>`, and that when wrapped objects are created by calling the constructor from Python, how they are held is determined by the HeldType parameter to `class_<...>` instances.
[endsect]
[section Function `register_ptr_to_python`]
``
template <class P>
void register_ptr_to_python()
``
[variablelist
[[Requires][`P` is [link concepts.dereferenceable Dereferenceable].]]
[[Effects][Allows conversions to-python of P instances. ]]
]
[endsect]
[section Example]
Here is an example of a module that contains a class A with virtual functions and some functions that work with boost::shared_ptr<A>.
In C++:
``
struct A
{
virtual int f() { return 0; }
};
shared_ptr<A> New() { return shared_ptr<A>( new A() ); }
int Ok( const shared_ptr<A>& a ) { return a->f(); }
int Fail( shared_ptr<A>& a ) { return a->f(); }
struct A_Wrapper: A
{
A_Wrapper(PyObject* self_): self(self_) {}
int f() { return call_method<int>(self, "f"); }
int default_f() { return A::f(); }
PyObject* self;
};
BOOST_PYTHON_MODULE(register_ptr)
{
class_<A, A_Wrapper>("A")
.def("f", &A::f, &A_Wrapper::default_f)
;
def("New", &New);
def("Ok", &Call);
def("Fail", &Fail);
register_ptr_to_python< shared_ptr<A> >();
}
``
In Python:
``
>>> from register_ptr import *
>>> a = A()
>>> Ok(a) # ok, passed as shared_ptr<A>
0
>>> Fail(a) # passed as shared_ptr<A>&, and was created in Python!
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: bad argument type for built-in operation
>>>
>>> na = New() # now "na" is actually a shared_ptr<A>
>>> Ok(a)
0
>>> Fail(a)
0
>>>
``
If shared_ptr<A> is registered as follows:
``
class_<A, A_Wrapper, shared_ptr<A> >("A")
.def("f", &A::f, &A_Wrapper::default_f)
;
``
There will be an error when trying to convert shared_ptr<A> to shared_ptr<A_Wrapper>:
``
>>> a = New()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: No to_python (by-value) converter found for C++ type: class boost::shared_ptr<struct A>
>>>
``
[endsect]

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[section boost/python/return_arg.hpp]
[section Introduction]
`return_arg` and `return_self` instantiations are models of [link concepts.callpolicies `CallPolicies`] which return the specified argument parameter (usually `*this`) of a wrapped (member) function.
[endsect]
[section Class `return_arg`]
[table
[[Parameter][Requirements][Description][Default]]
[[arg_pos][A positive compile-time constant of type `std::size_t`.][the position of the argument to be returned.][1]]
[[Base][A model of [link concepts.callpolicies `CallPolicies`]][Used for policy composition. Any `result_converter` it supplies will be overridden by `return_arg`, but its `precall` and `postcall` policies are composed as described here [link concepts.callpolicies `CallPolicies`].][default_call_policies]]
]
``
namespace boost { namespace python
{
template <size_t arg_pos=1, class Base = default_call_policies>
struct return_arg : Base
{
static PyObject* postcall(PyObject*, PyObject* result);
struct result_converter{ template <class T> struct apply; };
template <class Sig> struct extract_return_type : mpl::at_c<Sig, arg_pos>{};
};
}}
``
[endsect]
[section Class `return_arg` static functions]
``PyObject* postcall(PyObject* args, PyObject* result);``
[variablelist
[[Requires][`PyTuple_Check(args) != 0` and `PyTuple_Size(args) != 0`]]
[[Returns][PyTuple_GetItem(args,arg_pos-1)]]
]
[endsect]
[section Class template `return_self`]
``
namespace boost { namespace python
{
template <class Base = default_call_policies>
struct return_self
: return_arg<1,Base>
{};
}}
``
[endsect]
[section Example]
C++ module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_arg.hpp>
struct Widget
{
Widget() :sensitive_(true){}
bool get_sensitive() const { return sensitive_; }
void set_sensitive(bool s) { this->sensitive_ = s; }
private:
bool sensitive_;
};
struct Label : Widget
{
Label() {}
std::string get_label() const { return label_; }
void set_label(const std::string &l){ label_ = l; }
private:
std::string label_;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(return_self_ext)
{
class_<widget>("Widget")
.def("sensitive", &Widget::get_sensitive)
.def("sensitive", &Widget::set_sensitive, return_self<>())
;
class_<Label, bases<Widget> >("Label")
.def("label", &Label::get_label)
.def("label", &Label::set_label, return_self<>())
;
}
``
Python code:
``
>>> from return_self_ext import *
>>> l1 = Label().label("foo").sensitive(false)
>>> l2 = Label().sensitive(false).label("foo")
``
[endsect]
[endsect]

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[section boost/python/return_by_value.hpp]
[section Class `return_by_value`]
`return_by_value` is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning any reference or value type such that the return value is copied into a new Python object.
``
namespace boost { namespace python
{
struct return_by_value
{
template <class T> struct apply;
};
}}
``
[endsect]
[section Class `return_by_value` metafunctions]
``template <class T> struct apply``
[variablelist
[[Returns][`typedef to_python_value<T> type;`]]
]
[endsect]
[section Example]
In C++:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_by_value.hpp>
#include <boost/python/return_value_policy.hpp>
// classes to wrap
struct Bar { };
Bar global_bar;
// functions to wrap:
Bar b1();
Bar& b2();
Bar const& b3();
// Wrapper code
using namespace boost::python;
template <class R>
void def_void_function(char const* name, R (*f)())
{
def(name, f, return_value_policy<return_by_value>());
}
BOOST_PYTHON_MODULE(my_module)
{
class_<Bar>("Bar");
def_void_function("b1", b1);
def_void_function("b2", b2);
def_void_function("b3", b3);
}
``
Python code:
``
>>> from my_module import *
>>> b = b1() # each of these calls
>>> b = b2() # creates a brand
>>> b = b3() # new Bar object
``
[endsect]
[endsect]

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[section boost/python/return_internal_reference.hpp]
[section Introduction]
`return_internal_reference` instantiations are models of [link concepts.callpolicies `CallPolicies`] which allow pointers and references to objects held internally by a free or member function argument or from the target of a member function to be returned safely without making a copy of the referent. The default for its first template argument handles the common case where the containing object is the target (`*this`) of a wrapped member function.
[endsect]
[section Class template `return_internal_reference`]
[table
[[Parameter][Requirements][Description][Default]]
[[owner_arg][A positive compile-time constant of type `std::size_t`.][The index of the parameter which contains the object to which the reference or pointer is being returned. If used to wrap a member function, parameter 1 is the target object (`*this`). Note that if the target Python object type doesn't support weak references, a Python TypeError exception will be raised when the function being wrapped is called.][]]
[[Base][A model of [link concepts.callpolicies `CallPolicies`]][Used for policy composition. Any `result_converter` it supplies will be overridden by `return_internal_reference`, but its `precall` and `postcall` policies are composed as described here [link concepts.callpolicies `CallPolicies`].][default_call_policies]]
]
``
namespace boost { namespace python
{
template <std::size_t owner_arg = 1, class Base = default_call_policies>
struct return_internal_reference : Base
{
static PyObject* postcall(PyObject*, PyObject* result);
typedef reference_existing_object result_converter;
};
}}
``
[endsect]
[section Class `return_internal_reference` static functions]
``PyObject* postcall(PyObject* args, PyObject* result);``
[variablelist
[[Requires][`PyTuple_Check(args) != 0`]]
[[Returns][[link function_invocation_and_creation.models_of_callpolicies.boost_python_with_custodian_and_.class_with_custodian_and_ward_st `with_custodian_and_ward_postcall::postcall(args, result)`]]]
]
[endsect]
[section Example]
C++ module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_internal_reference.hpp>
class Bar
{
public:
Bar(int x) : x(x) {}
int get_x() const { return x; }
void set_x(int x) { this->x = x; }
private:
int x;
};
class Foo
{
public:
Foo(int x) : b(x) {}
// Returns an internal reference
Bar const& get_bar() const { return b; }
private:
Bar b;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(internal_refs)
{
class_<Bar>("Bar", init<int>())
.def("get_x", &Bar::get_x)
.def("set_x", &Bar::set_x)
;
class_<Foo>("Foo", init<int>())
.def("get_bar", &Foo::get_bar
, return_internal_reference<>())
;
}
``
Python code:
``
>>> from internal_refs import *
>>> f = Foo(3)
>>> b1 = f.get_bar()
>>> b2 = f.get_bar()
>>> b1.get_x()
3
>>> b2.get_x()
3
>>> b1.set_x(42)
>>> b2.get_x()
42
``
[endsect]
[endsect]

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[section boost/python/return_opaque_pointer.hpp]
[section Class `return_opaqe_pointer`]
return_opaque_pointer is a model of [link concepts.resultconverter.resultconvertergenerator_concept ResultConverterGenerator] which can be used to wrap C++ functions returning pointers to undefined types such that the return value is copied into a new Python object.
In addition to specifying the `return_opaque_pointer` policy the [link to_from_python_type_conversion.boost_python_opaque_pointer_conv.macro_boost_python_opaque_specia `BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID`] macro must be used to define specializations for the [link utility_and_infrastructure.boost_python_type_id_hpp.functions `type_id`] function on the type pointed to by returned pointer.
``
namespace boost { namespace python
{
struct return_opaque_pointer
{
template <class R> struct apply;
};
}}
``
[endsect]
[section Class `return_opaque_pointer` metafunctions]
``template <class T> struct apply``
[variablelist
[[Returns][`detail::opaque_conversion_holder<R> type;`]]
]
[endsect]
[section Example]
In C++:
``
# include <boost/python/return_opaque_pointer.hpp>
# include <boost/python/def.hpp>
# include <boost/python/module.hpp>
# include <boost/python/return_value_policy.hpp>
typedef struct opaque_ *opaque;
opaque the_op = ((opaque) 0x47110815);
opaque get () { return the_op; }
void use (opaque op) {
if (op != the_op)
throw std::runtime_error (std::string ("failed"));
}
void failuse (opaque op) {
if (op == the_op)
throw std::runtime_error (std::string ("success"));
}
BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(opaque_)
namespace bpl = boost::python;
BOOST_PYTHON_MODULE(opaque_ext)
{
bpl::def (
"get", &::get, bpl::return_value_policy<bpl::return_opaque_pointer>());
bpl::def ("use", &::use);
bpl::def ("failuse", &::failuse);
}
``
Python code:
``
"""
>>> from opaque_ext import *
>>> #
>>> # Check for correct conversion
>>> use(get())
>>> failuse(get())
Traceback (most recent call last):
...
RuntimeError: success
>>> #
>>> # Check that there is no conversion from integers ...
>>> use(0)
Traceback (most recent call last):
...
TypeError: bad argument type for built-in operation
>>> #
>>> # ... and from strings to opaque objects
>>> use("")
Traceback (most recent call last):
...
TypeError: bad argument type for built-in operation
"""
def run(args = None):
import sys
import doctest
if args is not None:
sys.argv = args
return doctest.testmod(sys.modules.get(__name__))
if __name__ == '__main__':
print "running..."
import sys
sys.exit(run()[0])
``
[endsect]
[endsect]

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[section boost/python/return_value_policy.hpp]
[section Introduction]
return_value_policy instantiations are simply models of [link concepts.callpolicies `CallPolicies`] which are composed of a [link concepts.resultconverter.resultconvertergenerator_concept `ResultConverterGenerator`] and optional `Base` [link concepts.callpolicies `CallPolicies`].
[endsect]
[section Class template `return_value_policy`]
[table
[[Parameter][Requirements][Default]]
[[ResultConverterGenerator][A model of [link concepts.resultconverter.resultconvertergenerator_concept `ResultConverterGenerator`]][]]
[[Base][A model of [link concepts.callpolicies `CallPolicies`]][default_call_policies]]
]
``
namespace boost { namespace python
{
template <class ResultConverterGenerator, class Base = default_call_policies>
struct return_value_policy : Base
{
typedef ResultConverterGenerator result_converter;
};
}}
``
[endsect]
[section Example]
C++ module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/copy_const_reference.hpp>
#include <boost/python/return_value_policy.hpp>
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar const& get_bar() const { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_<Bar>("Bar");
class_<Foo>("Foo", init<int>())
.def("get_bar", &Foo::get_bar
, return_value_policy<copy_const_reference>())
;
}
``
Python code:
``
>>> from my_module import *
>>> f = Foo(3) # create a Foo object
>>> b = f.get_bar() # make a copy of the internal Bar object
``
[endsect]
[endsect]

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[section boost/python/scope.hpp]
[section Introduction]
Defines facilities for querying and controlling the Python scope (namespace) which will contain new wrapped classes and functions.
[endsect]
[section Class `scope`]
The scope class has an associated global Python object which controls the Python namespace in which new extension classes and wrapped functions will be defined as attributes. Default-constructing a new scope object binds it to the associated global Python object. Constructing a scope object with an argument changes the associated global Python object to the one held by the argument, until the lifetime of the scope object ends, at which time the associated global Python object reverts to what it was before the scope object was constructed.
``
namespace boost { namespace python
{
class scope : public object
{
public:
scope(scope const&);
scope(object const&);
scope();
~scope()
private:
void operator=(scope const&);
};
}}
``
[endsect]
[section Class scope constructors and destructor]
``
explicit scope(scope const& x);
explicit scope(object const& x);
``
Stores a reference to the current associated scope object, and sets the associated scope object to the one referred to by x.ptr(). The object base class is initialized with x.
``scope();``
Stores a reference to the current associated scope object. The object base class is initialized with the current associated scope object. Outside any module initialization function, the current associated Python object is None.
``~scope()``
Sets the current associated Python object to the stored object.
[endsect]
[section Example]
The following example shows how scope setting can be used to define nested classes.
C++ Module definition:
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/scope.hpp>
using namespace boost::python;
struct X
{
void f() {}
struct Y { int g() { return 42; } };
};
BOOST_PYTHON_MODULE(nested)
{
// add some constants to the current (module) scope
scope().attr("yes") = 1;
scope().attr("no") = 0;
// Change the current scope
scope outer
= class_<X>("X")
.def("f", &X::f)
;
// Define a class Y in the current scope, X
class_<X::Y>("Y")
.def("g", &X::Y::g)
;
}
``
Interactive Python:
``
>>> import nested
>>> nested.yes
1
>>> y = nested.X.Y()
>>> y.g()
42
``
[endsect]
[endsect]

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[section boost/python/slice.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/doc/2.3.3/api/slice-objects.html `slice`] type.
[endsect]
[section Class `slice`]
Exposes the extended slicing protocol by wrapping the built-in slice type. The semantics of the constructors and member functions defined below can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since `slice` is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `slice` instances as well.
``
namespace boost { namespace python
{
class slice : public object
{
public:
slice(); // create an empty slice, equivalent to [::]
template <typename Int1, typename Int2>
slice(Int1 start, Int2 stop);
template <typename Int1, typename Int2, typename Int3>
slice(Int1 start, Int2 stop, Int3 step);
// Access the parameters this slice was created with.
object start();
object stop();
object step();
// The return type of slice::get_indices()
template <typename RandomAccessIterator>
struct range
{
RandomAccessIterator start;
RandomAccessIterator stop;
int step;
};
template <typename RandomAccessIterator>
range<RandomAccessIterator>
get_indices(
RandomAccessIterator const& begin,
RandomAccessIterator const& end);
};
}}
``
[endsect]
[section Class `slice` constructors]
``slice();``
[variablelist
[[Effects][constructs a slice with default stop, start, and step values. Equivalent to the slice object created as part of the Python expression `base[::]`.]]
[[Throws][nothing]]
]
``
template <typename Int1, typename Int2>
slice(Int1 start, Int2 stop);
``
[variablelist
[[Requires][`start`, `stop`, and `step` are of type `slice_nil` or convertible to type `object`.]]
[[Effects][constructs a new slice with default step value and the provided start and stop values. Equivalent to the slice object created by the built-in Python function `slice(start,stop)`, or as part of the Python expression `base[start:stop]`.]]
[[Throws][`error_already_set` and sets a Python TypeError exception if no conversion is possible from the arguments to type object.]]
]
``
template <typename Int1, typename Int2, typename Int3>
slice(Int1 start, Int2 stop, Int3 step);
``
[variablelist
[[Requires][`start`, `stop`, and `step` are `slice_nil` or convertible to type `object`.]]
[[Effects][constructs a new slice with start stop and step values. Equivalent to the slice object created by the built-in Python function `slice(start,stop,step)`, or as part of the Python expression `base[start:stop:step]`.]]
[[Throws][`error_already_set` and sets a Python TypeError exception if no conversion is possible from the arguments to type object.]]
]
[endsect]
[section Class `slice` observer functions]
``
object slice::start() const;
object slice::stop() const;
object slice::step() const;
``
[variablelist
[[Effects][None]]
[[Throws][nothing]]
[[Returns][the parameter that the slice was created with. If the parameter was omitted or `slice_nil` was used when the slice was created, than that parameter will be a reference to `PyNone` and compare equal to a default-constructed object. In principal, any object may be used when creating a slice object, but in practice they are usually integers.]]
]
``
template <typename RandomAccessIterator>
slice::range<RandomAccessIterator>
slice::get_indices(
RandomAccessIterator const& begin,
RandomAccessIterator const& end) const;
``
[variablelist
[[Arguments][A pair of STL-conforming Random Access Iterators that form a half-open range.]]
[[Effects][Create a RandomAccessIterator pair that defines a fully-closed range within the `[begin,end)` range of its arguments. This function translates this slice's indices while accounting for the effects of any PyNone or negative indices, and non-singular step sizes.]]
[[Returns][a `slice::range` that has been initialized with a non-zero value of step and a pair of RandomAccessIterators that point within the range of this functions arguments and define a closed interval.]]
[[Throws][Raises a Python TypeError exception if any of this slice's arguments are neither references to PyNone nor convertible to int. Throws `std::invalid_argument` if the resulting range would be empty. You should always wrap calls to `slice::get_indices()` within `try { ...; } catch (std::invalid_argument) {}` to handle this case and take appropriate action.]]
[[Rationale][closed-interval: If an open interval were used, then for step size other than 1, the required state for the end iterator would point beyond the one-past-the-end position or before the beginning of the specified range.
exceptions on empty slice: It is impossible to define a closed interval over an empty range, so some other form of error checking would have to be used to prevent undefined behavior. In the case where the exception is not caught, it will simply be translated to Python by the default exception handling mechanisms. ]]
]
[endsect]
[section Example]
``
using namespace boost::python;
// Perform an extended slice of a Python list.
// Warning: extended slicing was not supported for built-in types prior
// to Python 2.3
list odd_elements(list l)
{
return l[slice(_,_,2)];
}
// Perform a summation over a slice of a std::vector.
double partial_sum(std::vector<double> const& Foo, const slice index)
{
slice::range<std::vector<double>::const_iterator> bounds;
try {
bounds = index.get_indices<>(Foo.begin(), Foo.end());
}
catch (std::invalid_argument) {
return 0.0;
}
double sum = 0.0;
while (bounds.start != bounds.stop) {
sum += *bounds.start;
std::advance( bounds.start, bounds.step);
}
sum += *bounds.start;
return sum;
}
``
[endsect]
[endsect]

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[section boost/python/ssize_t.hpp]
[section Introduction]
Python 2.5 introduces a new `Py_ssize_t` typedef and two related macros ([@http://www.python.org/dev/peps/pep-0353/ PEP 353]). The <boost/python/ssize_t.hpp> header imports these definitions into the `boost::python` namespace as `ssize_t`, `ssize_t_max`, and `ssize_t_min`. Appropriate definitions are provided for backward compatibility with previous Python versions.
[endsect]
[section Typedefs]
Imports `Py_ssize_t` into the `boost::python` namespace if available, or provides an appropriate typedef for backward compatibility:
``
#if PY_VERSION_HEX >= 0x02050000
typedef Py_ssize_t ssize_t;
#else
typedef int ssize_t;
#endif
``
[endsect]
[section Constants]
Imports `PY_SSIZE_T_MAX` and `PY_SSIZE_T_MIN` as constants into the `boost::python` namespace if available, or provides appropriate constants for backward compatibility:
``
#if PY_VERSION_HEX >= 0x02050000
ssize_t const ssize_t_max = PY_SSIZE_T_MAX;
ssize_t const ssize_t_min = PY_SSIZE_T_MIN;
#else
ssize_t const ssize_t_max = INT_MAX;
ssize_t const ssize_t_min = INT_MIN;
#endif
``
[endsect]
[endsect]

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[section boost/python/stl_iterator.hpp]
[section Introduction]
<boost/python/stl_iterator.hpp> provides types for creating C++ Iterators from [@http://www.python.org/doc/current/lib/typeiter.html Python iterables].
[endsect]
[section Class template `stl_input_iterator`]
Instances of `stl_input_iterator<T>` hold a Python iterator and adapt it for use with STL algorithms. `stl_input_iterator<T>` satisfies the requirements for an Input Iterator.
[table
[[Template Parameter][Requirements][Semantics][Default]]
[[ValueType][ValueType must be CopyConstructible.][Dereferencing an instance of `stl_input_iterator<ValueType>` will return an rvalue of type ValueType.][None]]
]
``
namespace boost { namespace python
{
template <class ValueType>
struct stl_input_iterator
{
typedef std::ptrdiff_t difference_type;
typedef ValueType value_type;
typedef ValueType* pointer;
typedef ValueType reference;
typedef std::input_iterator_tag iterator_category;
stl_input_iterator();
stl_input_iterator(object const& ob);
stl_input_iterator& operator++();
stl_input_iterator operator++(int);
ValueType operator*() const;
friend bool operator==(stl_input_iterator const& lhs, stl_input_iterator const& rhs);
friend bool operator!=(stl_input_iterator const& lhs, stl_input_iterator const& rhs);
private:
object it; // For exposition only
object ob; // For exposition only
};
}}
``
[endsect]
[section Class template `stl_input_iterator` constructors]
``
stl_input_iterator()
``
[variablelist
[[Effects][Creates a past-the-end input iterator, useful for signifying the end of a sequence. ]]
[[Postconditions][`this` is past-the-end]]
[[Throws][Nothing.]]
]
``stl_input_iterator(object const& ob)``
[variablelist
[[Effects][Calls ob.attr("__iter__")() and stores the resulting Python iterator object in this->it. Then, calls this->it.attr("next")() and stores the result in this->ob. If the sequence is exhausted, sets this->ob to object(). ]]
[[Postconditions][this is a dereferenceable or past-the-end.]]
]
[endsect]
[section Class template `stl_input_iterator` modifiers]
``
stl_input_iterator &operator++()
``
[variablelist
[[Effects][Calls this->it.attr("next")() and stores the result in this->ob. If the sequence is exhausted, sets this->ob to object(). ]]
[[Postconditions][this is a dereferenceable or past-the-end.]]
[[Returns][`*this`]]
]
``stl_input_iterator &operator++(int)``
[variablelist
[[Effects][`stl_input_iterator tmp = *this; ++*this; return tmp;`]]
[[Postconditions][this is a dereferenceable or past-the-end.]]
]
[endsect]
[section Class template `stl_input_iterator` observers]
``
ValueType operator*() const
``
[variablelist
[[Effects][Returns the current element in the sequence. ]]
[[Returns][`extract<ValueType>(this->ob);`]]
]
``
friend bool operator==(stl_input_iterator const& lhs, stl_input_iterator const& rhs)
``
[variablelist
[[Effects][Returns true if both iterators are dereferenceable or if both iterators are past-the-end, false otherwise. ]]
[[Returns][`(lhs.ob == object()) == (rhs.ob == object())`]]
]
``
friend bool operator!=(stl_input_iterator const& lhs, stl_input_iterator const& rhs)
``
[variablelist
[[Effects][Returns false if both iterators are dereferenceable or if both iterators are past-the-end, true otherwise. ]]
[[Returns][`!(lhs == rhs)`]]
]
[endsect]
[section Example]
``
#include <boost/python/object.hpp>
#include <boost/python/stl_iterator.hpp>
#include <list>
using namespace boost::python;
std::list<int> sequence_to_int_list(object const& ob)
{
stl_input_iterator<int> begin(ob), end;
return std::list<int>(begin, end);
}
``
[endsect]
[endsect]

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[section boost/python/str.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/dev/doc/devel/lib/string-methods.html `str`] type.
[endsect]
[section Class `str`]
Exposes the [@http://www.python.org/dev/doc/devel/lib/string-methods.html string methods] of Python's built-in `str` type. The semantics of the constructors and member functions defined below, except for the two-argument constructors which construct str objects from a range of characters, can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since str is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `str` instances as well.
``
namespace boost { namespace python
{
class str : public object
{
public:
str(); // new str
str(char const* s); // new str
str(char const* start, char const* finish); // new str
str(char const* start, std::size_t length); // new str
template <class T>
explicit str(T const& other);
str capitalize() const;
template <class T>
str center(T const& width) const;
template<class T>
long count(T const& sub) const;
template<class T1, class T2>
long count(T1 const& sub,T2 const& start) const;
template<class T1, class T2, class T3>
long count(T1 const& sub,T2 const& start, T3 const& end) const;
object decode() const;
template<class T>
object decode(T const& encoding) const;
template<class T1, class T2>
object decode(T1 const& encoding, T2 const& errors) const;
object encode() const;
template <class T>
object encode(T const& encoding) const;
template <class T1, class T2>
object encode(T1 const& encoding, T2 const& errors) const;
template <class T>
bool endswith(T const& suffix) const;
template <class T1, class T2>
bool endswith(T1 const& suffix, T2 const& start) const;
template <class T1, class T2, class T3>
bool endswith(T1 const& suffix, T2 const& start, T3 const& end) const;
str expandtabs() const;
template <class T>
str expandtabs(T const& tabsize) const;
template <class T>
long find(T const& sub) const;
template <class T1, class T2>
long find(T1 const& sub, T2 const& start) const;
template <class T1, class T2, class T3>
long find(T1 const& sub, T2 const& start, T3 const& end) const;
template <class T>
long index(T const& sub) const;
template <class T1, class T2>
long index(T1 const& sub, T2 const& start) const;
template <class T1, class T2, class T3>
long index(T1 const& sub, T2 const& start, T3 const& end) const;
bool isalnum() const;
bool isalpha() const;
bool isdigit() const;
bool islower() const;
bool isspace() const;
bool istitle() const;
bool isupper() const;
template <class T>
str join(T const& sequence) const;
template <class T>
str ljust(T const& width) const;
str lower() const;
str lstrip() const;
template <class T1, class T2>
str replace(T1 const& old, T2 const& new_) const;
template <class T1, class T2, class T3>
str replace(T1 const& old, T2 const& new_, T3 const& maxsplit) const;
template <class T>
long rfind(T const& sub) const;
template <class T1, class T2>
long rfind(T1 const& sub, T2 const& start) const;
template <class T1, class T2, class T3>
long rfind(T1 const& sub, T2 const& start, T3 const& end) const;
template <class T>
long rindex(T const& sub) const;
template <class T1, class T2>
long rindex(T1 const& sub, T2 const& start) const;
template <class T1, class T2, class T3>
long rindex(T1 const& sub, T2 const& start, T3 const& end) const;
template <class T>
str rjust(T const& width) const;
str rstrip() const;
list split() const;
template <class T>
list split(T const& sep) const;
template <class T1, class T2>
list split(T1 const& sep, T2 const& maxsplit) const;
list splitlines() const;
template <class T>
list splitlines(T const& keepends) const;
template <class T>
bool startswith(T const& prefix) const;
template <class T1, class T2>
bool startswidth(T1 const& prefix, T2 const& start) const;
template <class T1, class T2, class T3>
bool startswidth(T1 const& prefix, T2 const& start, T3 const& end) const;
str strip() const;
str swapcase() const;
str title() const;
template <class T>
str translate(T const& table) const;
template <class T1, class T2>
str translate(T1 const& table, T2 const& deletechars) const;
str upper() const;
};
}}
``
[endsect]
[section Example]
``
using namespace boost::python;
str remove_angle_brackets(str x)
{
return x.strip('<').strip('>');
}
``
[endsect]
[endsect]

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[section boost/python/to_python_converter.hpp]
[section Introduction]
`to_python_converter` registers a conversion from objects of a given C++ type into a Python object.
[endsect]
[section Class template `to_python_converter`]
`to_python_converter` adds a wrapper around a static member function of its second template parameter, handling low-level details such as insertion into the converter registry.
In the table below, x denotes an object of type T
[table
[[Parameter][Requirements][Description]]
[[T][][The C++ type of the source object in the conversion]]
[[Conversion][`PyObject* p = Conversion::convert(x)`,
`if p == 0`, `PyErr_Occurred() != 0`.][A class type whose static member function convert does the real work of the conversion.]]
[[bool has_get_pytype=false][`PyTypeObject const * p = Conversion::get_pytype()`]
[Optional member - if Conversion has `get_pytype` member supply `true` for this parameters. If present `get_pytype` is used to document the return type of functions using this conversion. The `get_pytype` may be implemented using the classes and functions from pytype_function.hpp NOTE : For backward compatibility this parameter may be passed after checking if BOOST_PYTHON_SUPPORTS_PY_SIGNATURES is defined (see [link function_invocation_and_creation.function_documentation.boost_python_pytype_function_hpp.example here]).]
]]
``
namespace boost { namespace python
{
template <class T, class Conversion, bool convertion_has_get_pytype_member=false>
struct to_python_converter
{
to_python_converter();
};
}}
``
[section Class template `to_python_converter` constructor]
``to_python_converter();``
[variablelist
[[Effects][Registers a `to_python` converter which uses `Conversion::convert()` to do its work.]]
]
[endsect]
[endsect]
[section Example]
This example presumes that someone has implemented the standard noddy example module from the Python documentation, and placed the corresponding declarations in "noddy.h". Because noddy_NoddyObject is the ultimate trivial extension type, the example is a bit contrived: it wraps a function for which all information is contained in the type of its return value.
In C++:
``
#include <boost/python/reference.hpp>
#include <boost/python/module.hpp>
#include "noddy.h"
struct tag {};
tag make_tag() { return tag(); }
using namespace boost::python;
struct tag_to_noddy
{
static PyObject* convert(tag const& x)
{
return PyObject_New(noddy_NoddyObject, &noddy_NoddyType);
}
static PyTypeObject const* get_pytype()
{
return &noddy_NoddyType;
}
};
BOOST_PYTHON_MODULE(to_python_converter)
{
def("make_tag", make_tag);
to_python_converter<tag, tag_to_noddy, true>(); //"true" because tag_to_noddy has member get_pytype
}
``
In Python:
``
>>> import to_python_converter
>>> def always_none():
... return None
...
>>> def choose_function(x):
... if (x % 2 != 0):
... return to_python_converter.make_tag
... else:
... return always_none
...
>>> a = [ choose_function(x) for x in range(5) ]
>>> b = [ f() for f in a ]
>>> type(b[0])
<type 'NoneType'>
>>> type(b[1])
<type 'Noddy'>
>>> type(b[2])
<type 'NoneType'>
>>> type(b[3])
<type 'Noddy'>
``
[endsect]
[endsect]

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[section boost/python/to_python_indirect.hpp]
[section Introduction]
<boost/python/to_python_indirect.hpp> supplies a way to construct new Python objects that hold wrapped C++ class instances via a pointer or smart pointer.
[endsect]
[section Class `to_python_indirect`]
Class template `to_python_indirect` converts objects of its first argument type to python as extension class instances, using the ownership policy provided by its 2nd argument.
[table
[[Parameter][Requirements][Description]]
[[T][Either `U cv&` (where cv is any optional cv-qualification) or a [link concepts.dereferenceable Dereferenceable] type such that `*x` is convertible to `U const&`, where `U` is a class type. ][`A` type deferencing a C++ class exposed to Python using class template [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel `class_`]. ]]
[[MakeHolder][`h = MakeHolder::execute(p);` ][A class whose static `execute()` creates an `instance_holder`. ]]
]
Instantiations of to_python_indirect are models of [link concepts.resultconverter `ResultConverter`].
``
namespace boost { namespace python
{
template <class T, class MakeHolder>
struct to_python_indirect
{
static bool convertible();
PyObject* operator()(T ptr_or_reference) const;
private:
static PyTypeObject* type();
};
}}
``
[endsect]
[section Class `to_python_indirect` observers]
``PyObject* operator()(T x) const;``
[variablelist
[[Requires][`x` refers to an object (if it is a pointer type, it is non-null). `convertible() == true`.]]
[[Effects][Creates an appropriately-typed Boost.Python extension class instance, uses MakeHolder to create an instance_holder from x, installs the instance_holder in the new extension class instance, and returns a pointer to it.]]
]
[endsect]
[section Class `to_python_indirect` statics]
``bool convertible()``
[variablelist
[[Effects][Returns true iff any module has registered a Python type corresponding to U. ]]
]
[endsect]
[endsect]
[section Example]
This example replicates the functionality of [link function_invocation_and_creation.models_of_resultconvertergenerat.boost_python_reference_existing_.class_reference_existing_object `reference_existing_object`], but without some of the compile-time error checking.
``
struct make_reference_holder
{
typedef boost::python::objects::instance_holder* result_type;
template <class T>
static result_type execute(T* p)
{
return new boost::python::objects::pointer_holder<T*, T>(p);
}
};
struct reference_existing_object
{
// metafunction returning the ResultConverter
template <class T>
struct apply
{
typedef boost::python::to_python_indirect<T,make_reference_holder> type;
};
};
``
[endsect]
[endsect]

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[section boost/python/to_python_value.hpp]
[section Introduction]
`to_python_value` is a model of [link concepts.resultconverter ResultConverter] which copies its argument into a new Python object.
[endsect]
[section Class template `to_python_value`]
``
namespace boost { namespace python
{
template <class T>
struct to_python_value
{
typedef typename add_reference<
typename add_const<T>::type
>::type argument_type;
static bool convertible();
PyObject* operator()(argument_type) const;
};
}}
``
[endsect]
[section Class `to_python_value` observers]
``static bool convertible();``
[variablelist
[[Returns][`true` iff a converter has been registered which can convert `T` to python by-value. ]]
]
``PyObject* operator()(argument_type x) const;``
[variablelist
[[Requires][`convertible() == true`]]
[[Effects][converts `x` to python]]
[[Returns][the resulting Python object iff a converter for `T` has been registered, `0` otherwise. ]]
]
[endsect]
[endsect]

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[chapter Topics
[quickbook 1.7]
]
[include calling.qbk]
[include pickle.qbk]
[include indexing.qbk]

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[section boost/python/tuple.hpp]
[section Introduction]
Exposes a [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] for the Python [@http://www.python.org/doc/current/tut/node7.html#SECTION007300000000000000000`tuple`] type.
[endsect]
[section Class `tuple`]
Exposes the interface of Python's built-in tuple type. The semantics of the constructors and member functions defined below can be fully understood by reading the [link concepts.objectwrapper.typewrapper_concept_requirements TypeWrapper] concept definition. Since tuple is publicly derived from [link object_wrappers.boost_python_object_hpp.class_object `object`], the public `object` interface applies to `tuple` instances as well.
``
namespace boost { namespace python
{
class tuple : public object
{
// tuple() -> an empty tuple
tuple();
// tuple(sequence) -> tuple initialized from sequence's items
template <class T>
explicit tuple(T const& sequence)
};
}}
``
[endsect]
[section Function `make_tuple`]
``
namespace boost { namespace python
{
tuple make_tuple();
template <class A0>
tuple make_tuple(A0 const& a0);
template <class A0, class A1>
tuple make_tuple(A0 const& a0, A1 const& a1);
...
template <class A0, class A1,...class An>
tuple make_tuple(A0 const& a0, A1 const& a1,...An const& an);
}}
``
[variablelist
[[Effect][Constructs a new tuple object composed of `object(a0),
object(a0),...object(an)`. ]]
]
[endsect]
[section Example]
``
using namespace boost::python;
tuple head_and_tail(object sequence)
{
return make_tuple(sequence[0],sequence[-1]);
}
``
[endsect]
[endsect]

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[section boost/python/type_id.hpp]
[section Introduction]
<boost/python/type_id.hpp> provides types and functions for runtime type identification like those of of `<typeinfo>`. It exists mostly to work around certain compiler bugs and platform-dependent interactions with shared libraries.
[endsect]
[section Class template `type_info`]
`type_info` instances identify a type. As `std::type_info` is specified to (but unlike its implementation in some compilers), `boost::python::type_info` never represents top-level references or cv-qualification (see section 5.2.8 in the C++ standard). Unlike `std::type_info`, `boost::python::type_info` instances are copyable, and comparisons always work reliably across shared library boundaries.
``
namespace boost { namespace python
{
class type_info : totally_ordered<type_info>
{
public:
// constructor
type_info(std::type_info const& = typeid(void));
// comparisons
bool operator<(type_info const& rhs) const;
bool operator==(type_info const& rhs) const;
// observers
char const* name() const;
};
}}
``
[section Class template `type_info` constructor]
``type_info(std::type_info const& = typeid(void));``
[variablelist
[[Effects][constructs a `type_info` object which identifies the same type as its argument.]]
[[Rationale][Since it is occasionally necessary to make an array of `type_info` objects a benign default argument is supplied. Note: this constructor does not correct for non-conformance of compiler `typeid()` implementations. See `type_id`, below.]]
]
[endsect]
[section Class template `type_info` comparison]
``bool operator<(type_info const &rhs) const;``
[variablelist
[[Effects][yields a total order over `type_info` objects.]]
]
``bool operator==(type_info const &rhs) const;``
[variablelist
[[Returns][`true` iff the two values describe the same type.]]
[[Note][The use of `totally_ordered<type_info>` as a private base class supplies operators `<=`, `>=`, `>`, and `!=`]]
]
[endsect]
[section Class template `type_info` observers]
``
char const* name() const;
``
[variablelist
[[Returns][The result of calling `name()` on the argument used to construct the object.]]
]
[endsect]
[endsect]
[section Functions]
``
std::ostream& operator<<(std::ostream&s, type_info const&x);
``
[variablelist
[[Effects][Writes a description of the type described by to `x` into s.]]
[[Rationale][Not every C++ implementation provides a truly human-readable `type_info::name()` string, but for some we may be able to decode the string and produce a reasonable representation.]]
[[Note][On some non-conforming C++ implementations, the code is not actually as simple as described above; the semantics are adjusted to work as-if the C++ implementation were conforming.]]
]
``
template <class T> type_info type_id()
``
[variablelist
[[Returns][`type_info(typeid(T))`]]
[[Note][On some non-conforming C++ implementations, the code is not actually as simple as described above; the semantics are adjusted to work as-if the C++ implementation were conforming.]]
]
[endsect]
[section Example]
The following example, though silly, illustrates how the type_id facility might be used
``
#include <boost/python/type_id.hpp>
// Returns true iff the user passes an int argument
template <class T>
bool is_int(T x)
{
using boost::python::type_id;
return type_id<T>() == type_id<int>();
}
``
[endsect]
[endsect]

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[chapter Utility and Infrastructure
[quickbook 1.7]
]
[include has_back_reference.qbk]
[include instance_holder.qbk]
[include pointee.qbk]
[include handle.qbk]
[include type_id.qbk]
[include ssize_t.qbk]

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[section boost/python/with_custodian_and_ward.hpp]
[section Introduction]
This header provides facilities for establishing a lifetime dependency between two of a function's Python argument or result objects. The ward object will not be destroyed until after the custodian as long as the custodian object supports [@http://www.python.org/doc/current/lib/module-weakref.html weak references] (Boost.Python extension classes all support weak references). If the custodian object does not support weak references and is not `None`, an appropriate exception will be thrown. The two class templates `with_custodian_and_ward` and `with_custodian_and_ward_postcall` differ in the point at which they take effect.
In order to reduce the chance of inadvertently creating dangling pointers, the default is to do lifetime binding before the underlying C++ object is invoked. However, before invocation the result object is not available, so `with_custodian_and_ward_postcall` is provided to bind lifetimes after invocation. Also, if a C++ exception is thrown after `with_custodian_and_ward<>::precall` but before the underlying C++ object actually stores a pointer, the lifetime of the custodian and ward objects will be artificially bound together, so one might choose `with_custodian_and_ward_postcall` instead, depending on the semantics of the function being wrapped.
Please note that this is not the appropriate tool to use when wrapping functions which transfer ownership of a raw pointer across the function-call boundary. Please see the FAQ if you want to do that.
[endsect]
[section Class `with_custodian_and_ward`]
[table
[[Parameter][Requirements][Description][Default]]
[[custodian][ A positive compile-time constant of `type std::size_t`. ][ The 1-based index of the parameter which is the dependency in the lifetime relationship to be established. If used to wrap a member function, parameter 1 is the target object (`*this`). Note that if the target Python object type doesn't support weak references, a Python TypeError exception will be raised when the C++ object being wrapped is called. ][]]
[[ward][ A positive compile-time constant of type `std::size_t`. ][ The 1-based index of the parameter which is the dependent in the lifetime relationship to be established. If used to wrap a member function, parameter 1 is the target object (`*this`). ][]]
[[Base][ A model of [link concepts.callpolicies `CallPolicies`]][ Used for policy [link concepts.callpolicies.callpolicies_composition composition]. ][default_call_policies]]
]
``
namespace boost { namespace python
{
template <std::size_t custodian, std::size_t ward, class Base = default_call_policies>
struct with_custodian_and_ward : Base
{
static bool precall(PyObject* args);
};
}}``
[endsect]
[section Class `with_custodian_and_ward` static functions]
``bool precall(PyObject* args);``
[variablelist
[[Requires][`PyTuple_Check(args) != 0`]]
[[Effects][Makes the lifetime of the argument indicated by ward dependent on the lifetime of the argument indicated by custodian. ]]
[[Returns][false and PyErr_Occurred() != 0 upon failure, true otherwise.]]
]
[endsect]
[section Class `with_custodian_and_ward_postcall`]
[table
[[Parameter][Requirements][Description][Default]]
[[custodian][ A positive compile-time constant of type `std::size_t`. ][ The index of the parameter which is the dependency in the lifetime relationship to be established. Zero indicates the result object; 1 indicates the first argument. If used to wrap a member function, parameter 1 is the target object (`*this`). Note that if the target Python object type doesn't support weak references, a Python TypeError exception will be raised when the C++ object being wrapped is called. ][]]
[[ward][ A positive compile-time constant of type `std::size_t`. ][ The index of the parameter which is the dependent in the lifetime relationship to be established. Zero indicates the result object; 1 indicates the first argument. If used to wrap a member function, parameter 1 is the target object (`*this`). ][]]
[[Base][ A model of [link concepts.callpolicies `CallPolicies`]][ Used for policy [link concepts.callpolicies.callpolicies_composition composition]. ][default_call_policies]]
]
``
namespace boost { namespace python
{
template <std::size_t custodian, std::size_t ward, class Base = default_call_policies>
struct with_custodian_and_ward_postcall : Base
{
static PyObject* postcall(PyObject* args, PyObject* result);
};
}}
``
[endsect]
[section Class `with_custodian_and_ward_postcall` static functions]
``PyObject *postcall(PyObject* args, PyObject* result);``
[variablelist
[[Requires][`PyTuple_Check(args) != 0`, `result != 0`]]
[[Effects][Makes the lifetime of the object indicated by ward dependent on the lifetime of the object indicated by custodian. ]]
[[Returns][`0` and `PyErr_Occurred() != 0` upon failure, `true` otherwise. ]]
]
[endsect]
[section Example]
The following example shows how `with_custodian_and_ward_postcall` is used by the library to implement `return_internal_reference`
``
template <std::size_t owner_arg = 1, class Base = default_call_policies>
struct return_internal_reference
: with_custodian_and_ward_postcall<0, owner_arg, Base>
{
typedef reference_existing_object result_converter;
};
``
[endsect]
[endsect]

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[section boost/python/wrapper.hpp]
[section Introduction]
To wrap a class T such that its virtual functions can be "overridden in Python"—so that the corresponding method of a Python derived class will be called when the virtual function is invoked from C++—you must create a C++ wrapper class derived from `T` that overrides those virtual functions so that they call into Python. This header contains classes that can be used to make that job easier.
[endsect]
[section Class `override`]
Encapsulates a Python override of a C++ virtual function. An override object either holds a callable Python object or `None`.
``
namespace boost
{
class override : object
{
public:
unspecified operator() const;
template <class A0>
unspecified operator(A0) const;
template <class A0, class A1>
unspecified operator(A0, A1) const;
...
template <class A0, class A1, ...class An>
unspecified operator(A0, A1, ...An) const;
};
};
``
[endsect]
[section Class `override` observer functions]
``
unspecified operator() const;
template <class A0>
unspecified operator(A0) const;
template <class A0, class A1>
unspecified operator(A0, A1) const;
...
template <class A0, class A1, ...class An>
unspecified operator(A0, A1, ...An) const;
``
[variablelist
[[Effects][If *this holds a callable Python object, it is invoked with the specified arguments in the manner specified here. Otherwise, throws [link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set].]]
[[Returns][An object of unspecified type that holds the Python result of the invocation and, when converted to a C++ type R, attempts to convert that result object to R. If that conversion fails, throws [link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set].]]
]
[endsect]
[section Class template `wrapper`]
Deriving your wrapper class from both `T` and `wrapper<T>` makes writing that derived class easier.
``
namespace boost
{
class wrapper
{
protected:
override get_override(char const* name) const;
};
};
``
[endsect]
[section Class template `wrapper` observer functions]
``override get_override(char const* name) const;``
[variablelist
[[Requires][name is a [link ntbs].]]
[[Returns][If `*this` is the C++ base class subobject of a Python derived class instance that overrides the named function, returns an override object that delegates to the Python override. Otherwise, returns an override object that holds `None`.]]
]
[endsect]
[section Example]
``
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/wrapper.hpp>
#include <boost/python/call.hpp>
using namespace boost::python;
// Class with one pure virtual function
struct P
{
virtual ~P(){}
virtual char const* f() = 0;
char const* g() { return "P::g()"; }
};
struct PCallback : P, wrapper<P>
{
char const* f()
{
return this->get_override("f")();
}
};
// Class with one non-pure virtual function
struct A
{
virtual ~A(){}
virtual char const* f() { return "A::f()"; }
};
struct ACallback : A, wrapper<A>
{
char const* f()
{
if (override f = this->get_override("f"))
return f();
return A::f();
}
char const* default_f() { return this->A::f(); }
};
BOOST_PYTHON_MODULE_INIT(polymorphism)
{
class_<PCallback,boost::noncopyable>("P")
.def("f", pure_virtual(&P::f))
;
class_<ACallback,boost::noncopyable>("A")
.def("f", &A::f, &ACallback::default_f)
;
}
``
[endsect]
[endsect]