Appendix C. Python 3: The Evolution of a Programming Language
Python 3.0 represents an evolution of the language that will not execute most older code that was written against the 2.x intepreters. This doesn’t mean that you won’t recognize the old code any more, or that “major” porting is required to make old code work under 3.x. In fact, the new syntax is quite similar to that of the past. However, when the
print statement no longer exists, it makes it easy to “break” the old code. In this appendix, we discuss
print and other 3.x changes, and we shed some light on the “required evolution” that Python must undergo to be better than it was before. Finally, we present a few migration tools that may help you make this transition.