A book for intermediate Python programmers is available at http://inventwithpython.org/pygame. It's free under a Creative Commons license, and aimed at beginners who know a little programming (but doesn't assume you know Python). It has the source code for 11 games (clones like Tetris, Nibbles, Simon, Connect Four, etc.) and explains how the source code for these games work.
You don't need to have read "Invent with Python" first to read this book. This book just assumes you aren't a complete beginner programmer.
(Pygame is an Python wrapper for SDL, and can be downloaded for free from pygame.org)