Python: Pocket Reference (Pocket Reference (O'Reilly))
I've recently had to make a similar transition for work reasons, and it's been pretty painful. For better or worse, Python has a very different philosophy and way of working than Perl, and getting used to that can be frustrating. The things I've found most useful have been
Personally, I found Dive Into Python annoying and patronising, but it's freely available online, so you can form your own judgment on that.