This comes from the fact that d2 is developed with two Mercurial branches, not build-time 2to3 conversion (which I dislike as ugly and not fully correct) nor single-source (which I dislike as ugly and hard to maintain :). PyPI does not work well with that workflow; see how unittest2 had to use a unittest2py3k project name. I think pip does the right thing if you upload project-X.Y-py3.tar.gz, I need to check that and if it works do a manual upload of 1.0a4-py3.