The Wingware editor from http://www.wingware.com is Python-specific with very good auto-completion for Python/Django/Zope, etc.
It has a built in Python shell to run snippets (or select and run) and support for Mercurial/Git, etc. and a built-in unittest/nose/doctest test runner. It's commercial though, but as it is written in Python, it's cross platform.
I bought it a while ago, and thought it looked dorky, but I've tried them all and keep coming back. Caveat that I am a Windows guy with no Emacs or Vim skills, so leveraging that was not an option. And the Mac version requires X Window and seems to be more glitchy.