MacPython is an excellent native Mac OS X port of Python (2.3 at present), complete with a simple yet powerful IDE that reminds me a lot of MPW for whatever reason.
Excellent debugging and module browsing make for easy development, and it includes a Python package manager to install several Mac-specific modules (like the Carbon wxWindows port).
Alas, the editor seems to have its own opinion as to tab handling (but it might be a preferences bug, since I run it as an unprivileged user).