Writing code for Python 3 and 2 isn't that difficult.
I've been doing it for a while now while working on a variety of different libraries for the Pyramid project, as well as hacking on WebOb which is Python 2 and 3.
Especially if you drop Python 3.2 and lower from the Py 3.x series you have very little trouble writing code that runs on both (with a shim or two here and there).
