MacPython DevelopersThe information here is specifically meant for people wanting to help develop MacPython itself, as opposed to people wanting the develop with MacPython.
First and foremost, you should probably join the PythonMac-SIG mailing list, where most of the developers hang out. See the community section for details.
MacPython-OSXMacPython-OSX is built in a rather standard way for a unix tool, so building it from source should not pose too many problems to a moderately experienced unix developer. See www.python.org for details on source access and such. You should read the file Mac/OSX/README after downloading or checking out the sources.
You need the Apple Developer Tools to build MacPython from source. These are a free download from Apple, (after registering for a free ADC membership), but it is a hefty 200 MB installer. See the Getting Started section of developer.apple.com for details.
MacPython-OS9MacPython-OS9 is considerably harder to build, you need the commercial CodeWarrior development environment from Metrowerks. You also need a library called GUSI, the Grand Unified Socket Interface, which provides unix-like sockets and file descriptors for I/O, by Matthias Neeracher. This library is free, though, and a copy adapted for Python can be found at the download page.
Even with these in place building is not trivial. After downloading a source distribution (or checking out from CVS) the file :Mac:Demo:building.html has information to get you on your way.
If you want to build only extension modules the situation is a lot simpler, though. You don't need to build everything from source, you just select the optional developer package in the installer and you are all set. Provided you have CodeWarrior, that is...
For MacPython 2.2, Corran Webster reported that it is not even necessary to buy the CodeWarrior C compiler to write MacPython extension modules: in many case Apple's free MPW tools work just fine. See his Compiling Python modules with MPW page for details.
Using the free OSX developer tools is not going to work for MacPython-OS9.
CVS Source accessThe MacPython sources live in the main Python CVS repository, so a single cvs checkout of the main Python repository suffices to build MacPython. See the developer section on www.python.org for details on checking out the Python sources.