python actually has reasonably good support for this via a single environment variable (PYTHONENV or PYTHONHOME, I think, it's been a while since I looked at this). The problem is that it overrides all the default search/path locations, and thus is missing the complete stdlib unless you copy everything into it. There's also the matter of binary modules that can not be shared between some interpreter versions (which feels like it begat Ubuntu's questionable python-dist symlink nightmare).