Good news, everyone: there is a nice, creative-commons licensed ( cc-by-nc ) book about python, even with a python3 version:
Think Python: http://www.greenteapress.com/thinkpython/. From the author of “How to think like a computer scientist”, Allen B. Downey. He initially wrote an (also free licensed) java book to improve the learning experience of his students, and a teacher made a python version out of it. The author has all source code examples linked on the book homepage and has a section in the book listing every single contributor who corrected an error or found a typo.
As soon as i have worked throug the complete book i will update this review. What i have seen so far was very impressive.