One word: Rope

It gives you all sort of semantic and refactoring awesomeness for python in emacs.

Thanks so much for posting that; it has been on my todo list for a while now to figure out a neat way of hooking virtualenv into emacs!

It's not about what Emacs can do for you, but what you can do for Emacs.

What can give me IDE-like popup completion for the current file using a live python interpreter beyond the scenes?

Rope :)

Why isn't there SLIME for Python?

Because Python isn't Lisp.

I don't think python particularly handles image based programming very well (not that all Lisps do this exclusively, just that they support it well enough for SLIME to make sense). Right now I have a load of code in Python which I'm constantly changing and reloading into my iPython session and it can be a bit of a pain, my files are littered with "reload(x)" statements just so when I reload one the others also get reloaded. I've tried the deep-reload extension to iPython without much success but maybe this will help in the future.