This updated version is also on the Rhodes Network: it is the newest one, but differs in places from printed 2012 copies that were made in July.
The official online book is at http://openbookproject.net/thinkcs/python/english3e/
Download a zip file of the html (consistent with the printed books) for offline use. (about 3 MB). Or you could use the updated version since the last book printing,
Download a pdf file(about 3 MB) e.g. for printing. This is usually a little stale, and is always uglier because it has been through Latex.
Get sources from the repository at https://code.launchpad.net/~thinkcspy-rle-team/thinkcspy/thinkcspy3-rle
The Interactive Edition by Brad Miller and David Ranum for use at Luther College is a derivative book that changes much of the content and emphasis. It also has some great features where you can write, execute, and visualize fragments of Python code inside the textbook. It could have been called the Hogwarts Magic Edition. Try it.