I've added Appendix A - Differences between Python 2 and 3 and Appendix B - Statements, Functions, and Methods Reference to the book. Quite a few people who have emailed me seem to be confused that the programs are in Python 3 (except for the Pygame programs, which are in Python 2). There aren't that many differences, and I've outlined them in Appendix A. Appendix B is a handy and quick guide to all the functions used in the book.