> It seems to me this is just a special case of the more general issue of building multiple versions of the
> same distribution, say with multiple versions of Python 2.  In general, anytime you change your build
> environment, you should start with no existing build directory.

Maybe Distutils could do that for you.

> Distutils doesn't keep track of every change you might make in a build environment between invocations
> of setup.py.

Could you detail what you mean with “change in a build environment”?  Timestamps are tracked, C headers dependencies too, changes to setup.py (and maybe setup.cfg too), so I think it wouldn’t be a stretch to also track the Python version used to run setup.py.  On the other hand, even with the same version there can be differences in the command-line options, the available modules (using Pythons with the same version from different virtual environments), etc.  Anyway, using one build directory per version (X.Y.Z) could easily solve a part of these issues.

What do people think?