Python 3 - Second Edition

45.2    The Leap to Python 3

In the following sections, we’ll describe the drastic version jump from Python 2 to Python 3. The special thing about version 3.0 is that it’s no longer backward compatible with older Python versions. This means that a program written for Python 2 most likely won’t run under Python 3. The break with backward compatibility allowed Python developers to remove long-dragged-along ugliness and inconsistency from the language, releasing an all-around renewed version of Python.

This section explains the main differences between Python versions 2 and 3.

Note

Python 3 also introduced many subtle changes—for example, to the interfaces of many modules in the standard library—that can’t all be explained here for obvious reasons. ...