The Biopython source code is kept under a version control system which allows multiple users from around the world to work on the same code base at the same time. We currently use git (developed by Linus Torvalds for Linux kernel development). Prior to September 2009, we used to use CVS.
An hourly updated CVS checkout of Biopython was available at http://biopython.open-bio.org/SRC/biopython and we intend to have this updated from git shortly.
Viewing git sources
Our current development git sources are available for viewing via GitHub:
This is the main repository. You can download these sources by clicking the Download link near the top of the page.
Getting a copy of the repository (called "cloning" in Git terminology) without GitHub account is very simple using the git command line tool:
git clone git://github.com/biopython/biopython.git
This command creates a local copy of the entire Biopython repository on your machine (your own personal copy of the official repository with its complete history). You can now make local changes and commit them to this local copy (although we advise you to use named branches for this, and keep the master branch in sync with the official Biopython code).
If you want other people to see your changes, however, you must publish your repository to a public server yourself (e.g. on GitHub).
See also GitUsage.
In order to make changes to the official repository, you will need a github account with collaborator status. Write CVS access is available for Biopython developers. This is normally given on a case by case basis, and the best place to discuss getting write access is on the Biopython Development mailing list.
Write access will of course be given to existing Biopython developers who had CVS commit rights.
Once you have access, see the instructions on GitUsage
Migration from CVS
Most of the other Open Bioinformatics Foundation projects migrated from CVS to Subversion (SVN). Biopython had been considering moving from CVS to SVN for a while, but instead moved to git. BioRuby also uses github.