Last but by no means least – books. Of course, there are a lot of really great books out there to buy or borrow. Due mainly to convenience and cost, I have concentrated my learning online but I have also used several very useful books.
The Self Taught Programmer – Cory Althoff
Good beginner level introduction. Useful because it also introduces some of the other skills you will need like Linux, Git etc.
Python Tricks the Book – Dan Bader
Intermediate level. You need to have some experience already to fully benefit from this book. This book gets back to basics and explains features in a unique way that really helps you understand how they work at a fundamental level.
Python Cookbook – David Beazley and Brian K Jones
Intermediate/advanced. Full disclosure – I have not read the entire book! I use this book more as a reference for when I come across particular features that I need to explore further.