The Python source code is stored in the Subversion, or SVN, version control system.
Anyone can check out a read-only copy of the source tree by using anonymous SVN. To check out the tree:
svn co http://svn.python.org/projects/python/trunk python
Running svn update will update the tree to the most recent version. Checkin messages and the accompanying diffs are sent to the python-checkins mailing list so that they get double-checked by the other developers. It's recommended that you subscribe to this list, especially if you've been granted write access to the source tree.
For information about SVN, see "Version Control with Subversion" at http://svnbook.red-bean.com/.
Write access to the Python SVN tree is not automatically granted, though there's no formal process to go through to get it. If the python-dev team knows who you are, whether through mailing list discussion, having submitted patches, or some other interaction, then you can ask for full SVN access. You'll need to have an SSH key, and provide it with your request.
If you're granted SVN write access, you have to follow a few simple rules.
To report a bug in Python, use the bug tracker. Don't report bugs by posting them to a mailing list or by sending them to a particular developer as a private e-mail; most likely the bug will end up buried under subsequent postings and e-mails and subsequently forgotten. Once a problem is recorded in the bug tracker, though, it's unlikely to be lost. It may sit unchanged for a while until someone gets around to looking at it, but before releases someone will go over the outstanding bugs and fix or close them. PEP 3, "Guidelines for Handling Bug Reports" explains the procedures for handling bugs once they've been reported.
Just like bugs, and for much the same reasons, patches should be submitted to the patch manager, and not through e-mail. Often a patch will need some modification before final acceptance, so be prepared to go through a few iterations before the patch is ready to be checked in.
Some conventions that should be followed when preparing a patch are:
SourceForge bug reports have long and ugly URLs:
This would be the link for bug #450000. A redirector has been set up on python.org, so a shorter URL for both bugs and patches is:
http://www.python.org/sf/<bug or patch ID>