What's the difference among these versions? Which one should I use?
In brief, the 2nd Edition uses Python 2, and will be gradually abandoned. The 3rd Edition is a Python 3 version derived from the 2nd Edition by Professor Peter Wentworth for use at Rhodes University in South Africa.
Our longer term goal is to faciliate your ability to derive your own custom version to best meet your local needs. We have begun work on an on-line tool called pybookbuilder for that purpose. In the mean time, you are free to use whichever version of the text most closely meets your needs.
-- Jeffrey Elkner