Use the indentation script pointed to and explained by this article: http://henry.precheur.org/2008/4/18/Indenting_Python_with_VI...

It is better than the default vim python autoindentation behavior.

Actually, I think vim comes with pretty good Python support by default. I'm using vim 7.1 and there's, for example, a good python.vim syntax file that came with.

You can find some goodies here: http://blog.sontek.net/2008/05/11/python-with-a-modular-ide-...