I was put onto a Python project at work so I started with the best quick reference I could find (wikipedia!) and then went from there.

Started at: http://en.wikipedia.org/wiki/Python_(programming_language) http://en.wikipedia.org/wiki/Python_syntax_and_semantics

Found most other details on here: http://www.python.org/dev/peps/ http://www.python.org/doc/

There's some good online tutorials to ease into some of the trickier details like metaclasses and descriptors.

I was already coding Ruby before this (and some LISP before that) so the whole dynamic language thing was familiar enough I could get away with mostly references. Your milage may vary :)