Several issues with urllib/urllib2 documentation regarding proxy usage:

1. The Macintosh proxy description in section 21.5.1 is out-of-date:

    "In a Macintosh environment, urlopen() will retrieve
     proxy information from Internet Config."

   Suggest something like:

    "In a Mac OS X environment, urlopen() will retrieve
     proxy information from the OS X System Configuration
     framework, which can be managed with the Network system
     preference panel." 

2. In general, urllib/urllib2 on Python 2 and urllib.request on Python 3
   are supposed to default to using the OS's proxy configuration on 
   Windows and OS X if not overridden by environment variables or
   if not supplied as an argument.  This is described in python 2 docs
   section 21.5.1. urllib2 has the same default behavior since under the
   covers it uses urllib's proxy functions.  But that behavior is not
   documented in 21.6 for urllib2 in the various spots where proxy is
   mentioned.

3. Likewise, the corresponding sections of the Python 3 documentation
   for urllib.request (section 20.5) do not mention the default system
   proxy configuration behavior and should since that code was carried
   over from Python 2 (although, at the moment, the OS X code is broken
   - see Issue7154).

I have attached a docs patch against the trunk.
Please provide your review comments. If its okay, I can commit it and
have the information (urllib2.rst) for the Python 3k too.

One comment:
+   :envvar:`<protocol>_proxy`.  In a Windows environment, if no proxy
+   environment variables are set, proxy settings are obtained from the
+   registry's Internet Settings section.  In a Mac OS X  environment, 
proxy
+   information is retrieved from from the OS X System Configuration 
Framework.

The "if no proxy environment variables are set" part applies to OS X as 
well so perhaps:

  If no proxy environment variables are set, in a Windows environment 
... and in a Mac OS X environment ... .

Otherwise looks good. Thanks!

Thanks for the comments.

Fixed and committed the changes trunk - 75478.
and merged into
release26-maint - 75479.
py3k - r75476
release31-maint - r75477