I found these very nice free downloadable Python books by Green Tea Press. Green Tea also offers other free books on Java, C++, OCaml and other subjects. I hope this info will be useful. Enjoy!

Think Python: How To Think Like a Computer Scientist

An introduction to programming using Python, one of the best programming languages for beginners.

Think Complexity: Exploring Complexity Science with Python

An introduction to algorithms and data structures in Python, including graphs and arrays, and complexity science, which includes small world graphs, scale-free networks, cellular automata, self-organized criticality, fractals, and agent-based models.

Think Stats: Probability and Statistics for Programmers

If you have basic skills in Python, you can use them to learn concepts in probability and statistics. This new book emphasizes simple techniques you can use to explore real data sets and answer interesting statistical questions.