I don't plan to write about every package I port, but there were some lessons learned from zope.tal that I thought I should mention. - Running 2to3 on your sources is a good way to identify places that need changing, but you'll have to revert most of the actual changes to keep it compatible with Python 2. I recently learned about a tool called python-modernize[1] that is basically 2to3 except it rewrites into a common Python 2 & 3 subset. I haven't checked it out yet, but it sounds promising [1] http://pypi.python.org/pypi/modernize - StringIO: while Python-3-style io.StringIO() and io.BytesIO() classes exist in Python 2.6+, you can't easily use either them as a replacement for StringIO.StringIO or cStringIO.StringIO. Why? Because people tend to mix native (ASCII-only) string literals with Unicode objects, and that's a no-no in Python 3 land. I didn't like the idea of importing unicode_literals from the __future__, or of dropping u'' prefixes everywhere. Partially because I'm not sure that would be enough -- str objects might make it all the way though the public API of zope.tal and suddenly code that used to work on Python 2 just fine would now explode. So I went with a conditional import -- from cStringIO import StringIO on Python 2 and from io import StringIO on Python 3. - tox/detox make it very easy to add just one more supported Python version -- edit tox.ini, run detox, fix tests. This works with PyPy too, not just Python 3.x! Marius Gedminas -- http://pov.lt/ -- Zope 3/BlueBream consulting and development