To check out the source code, go to the Source tab above and follow the instructions. To submit your patch, upload it to codereview.appspot.com using the upload.py script and add gvanrossum@gmail.com to the list of the reviewers (use the Publish+Mail link on the issue page).

Individual contributors need to fill out the Individual Contributor License Agreement. (Please use the electronic form at the bottom of the page.) It does not transfer copyright, it is actually a slightly modified version of the CLA for the apache software foundation.

For Corporate contributors, there's the Software Grant and Corporate Contributor License Agreement.

Google employees do not have to fill out one of these!