Python 3 is also not meant to run Python 2.x code. It's pretty trivial to port most code from Python 2.x to Python 3, but there's no real reason to do so unless you're writing a library or other project for other people to take advantage of.
It was intentionally done as a 'clean break' release; 2.x keeps doing the same stuff it used to do, and Python 3 changes a bunch of stuff which, in hindsight, makes sense (such as a distinction between 'stream of bytes' and 'string of text', vs. 'stream of bytes which may or may not be ascii text' and 'string of unicode text').
That said, there's no real benefit to moving an existing project/codebase from 2.x to 3.x, and it was never intended that there would be one. Python 3 is for new projects; Python 2.x is for existing projects, or new projects which need deployment in older environments.
