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<p>
Python can be built in a special “python debugging” configuration that
adds extra checks and instrumentation that can be very useful for developers
of extension modules. The data structures used by the debugging configuration
contain additional members, so <span class="bold"><strong>a Python executable
built with python debugging enabled cannot be used with an extension module
or library compiled without it, and vice-versa.</strong></span>
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<p>
Since pre-built “python debugging” versions of the Python executable
and libraries are not supplied with most distributions of Python, <a href="#ftn.building.python_debugging_builds.f0" class="footnote" name="building.python_debugging_builds.f0"><sup class="footnote">[5]</sup></a> and we didn't want to force our users to build them, Boost.Build
does not automatically enable python debugging in its <code class="computeroutput"><span class="identifier">debug</span></code>
build variant (which is the default). Instead there is a special build property
called <code class="computeroutput"><span class="identifier">python</span><span class="special">-</span><span class="identifier">debugging</span></code> that, when used as a build property,
will define the right preprocessor symbols and select the right libraries
to link with.
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<p>
On unix-variant platforms, the debugging versions of Python's data structures
will only be used if the symbol <code class="computeroutput"><span class="identifier">Py_DEBUG</span></code>
is defined. On many windows compilers, when extension modules are built with
the preprocessor symbol <code class="computeroutput"><span class="identifier">_DEBUG</span></code>,
Python defaults to force linking with a special debugging version of the
Python DLL. Since that symbol is very commonly used even when Python is not
present, Boost.Python temporarily undefines <code class="computeroutput"><span class="identifier">_DEBUG</span></code>
when <code class="computeroutput"><span class="identifier">Python</span><span class="special">.</span><span class="identifier">h</span></code> is #included from <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="identifier">detail</span><span class="special">/</span><span class="identifier">wrap_python</span><span class="special">.</span><span class="identifier">hpp</span></code> -
unless <code class="computeroutput"><span class="identifier">BOOST_DEBUG_PYTHON</span></code>
is defined. The upshot is that if you want “python debugging”and you
aren't using Boost.Build, you should make sure <code class="computeroutput"><span class="identifier">BOOST_DEBUG_PYTHON</span></code>
is defined, or python debugging will be suppressed.
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<div class="footnotes">
<br><hr style="width:100; text-align:left;margin-left: 0">
<div id="ftn.building.python_debugging_builds.f0" class="footnote"><p><a href="#building.python_debugging_builds.f0" class="para"><sup class="para">[5] </sup></a>
On Unix and similar platforms, a debugging python and associated libraries
are built by adding --with-pydebug when configuring the Python build. On
Windows, the debugging version of Python is generated by the "Win32
Debug" target of the Visual Studio project in the PCBuild subdirectory
of a full Python source code distribution.
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<td align="right"><div class="copyright-footer">Copyright © 2002-2015 David
Abrahams, Stefan Seefeld<br>Copyright © 2002-2015 David Abrahams, Stefan Seefeld<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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