Upgrade to tzdata2012i.

Also support GPG signature verification of updates, and fix remaining
pylint complaints.

The 2012i release of the tz data reflects the following changes recently
circulated on the tz mailing list:

* Cuba switches from DST [2012-11-04] at 01:00.  (Thanks to Steffen Thorsen.)

Change-Id: Ie81d395afa40aa217a0196aad8ca1f9a870bbc31

libc/tools/zoneinfo/generate

@@ -32,22 +32,22 @@ regions = ['africa', 'antarctica', 'asia', 'australasia', 'backward',
 
 
 def GetCurrentTzDataVersion():
-  return open('%s/tzdata' % bionic_libc_zoneinfo_dir).read().split('\0', 1)[0]
+  return open('%s/tzdata' % bionic_libc_zoneinfo_dir).read().split('\x00', 1)[0]
 
 
 def WriteSetupFile():
+  """Writes the list of zones that ZoneCompactor should process."""
   links = []
   zones = []
   for region in regions:
     for line in open('extracted/%s' % region):
       fields = line.split()
-      if len(fields) == 0:
-        continue
-      elif fields[0] == 'Link':
-        links.append('%s %s %s\n' % (fields[0], fields[1], fields[2]))
-        zones.append(fields[2])
-      elif fields[0] == 'Zone':
-        zones.append(fields[1])
+      if fields:
+        if fields[0] == 'Link':
+          links.append('%s %s %s\n' % (fields[0], fields[1], fields[2]))
+          zones.append(fields[2])
+        elif fields[0] == 'Zone':
+          zones.append(fields[1])
   zones.sort()
 
   setup = open('setup', 'w')
@@ -58,20 +58,34 @@ def WriteSetupFile():
   setup.close()
 
 
-def UpgradeTo(ftp, filename):
-  new_version = re.search('(tzdata.+)\.tar\.gz', filename).group(1)
+def Retrieve(ftp, filename):
+  ftp.retrbinary('RETR %s' % filename, open(filename, 'wb').write)
+
+
+def UpgradeTo(ftp, data_filename):
+  """Downloads and repackages the given data from the given FTP server."""
+
+  new_version = re.search('(tzdata.+)\\.tar\\.gz', data_filename).group(1)
+  signature_filename = '%s.sign' % data_filename
 
   # Switch to a temporary directory.
   tmp_dir = tempfile.mkdtemp('-tzdata')
   os.chdir(tmp_dir)
   print 'Created temporary directory "%s"...' % tmp_dir
 
-  print 'Downloading...'
-  ftp.retrbinary('RETR %s' % filename, open(filename, 'wb').write)
+  print 'Downloading data and signature...'
+  Retrieve(ftp, data_filename)
+  Retrieve(ftp, signature_filename)
+
+  print 'Verifying signature...'
+  # If this fails for you, you probably need to import Paul Eggert's public key:
+  # gpg --recv-keys ED97E90E62AA7E34
+  subprocess.check_call(['gpg', '--trusted-key=ED97E90E62AA7E34',
+                         '--verify', signature_filename, data_filename])
 
   print 'Extracting...'
   os.mkdir('extracted')
-  tar = tarfile.open(filename, 'r')
+  tar = tarfile.open(data_filename, 'r')
   tar.extractall('extracted')
 
   print 'Calling zic(1)...'
@@ -94,17 +108,15 @@ def UpgradeTo(ftp, filename):
 
 
 # Run with no arguments from any directory, with no special setup required.
+# See http://www.iana.org/time-zones/ for more about the source of this data.
 def main():
-  # URL from "Sources for Time Zone and Daylight Saving Time Data"
-  # http://www.twinsun.com/tz/tz-link.htm
-
   print 'Looking for new tzdata...'
   ftp = ftplib.FTP('ftp.iana.org')
   ftp.login()
   ftp.cwd('tz/releases')
   tzdata_filenames = []
   for filename in ftp.nlst():
-    if filename.startswith('tzdata20'):
+    if filename.startswith('tzdata20') and filename.endswith('.tar.gz'):
       tzdata_filenames.append(filename)
   tzdata_filenames.sort()