They aren't. And there are automatic tools for converting between them (2to3 and 3to2), along with those __future__ imports that Aaron mentioned: doing "from __

They aren't. And there are automatic tools for converting between them (2to3 and 3to2), along with those __future__ imports that Aaron mentioned: doing "from __future__ import print_function, unicode_literals, absolute_import, division" would give you most of the Python 3 syntax changes in Python 2. The "everything expects bytes" to "everything expects text" change is the biggest hurdle for a lot of projects.