You can write a setup.py with no version information specified, and vcversioner
will find a recent, properly-formatted VCS tag and extract a version from it.
It's much more convenient to be able to use your version control system's
tagging mechanism to derive a version number than to have to duplicate that
information all over the place. I eventually ended up copy-pasting the same
code into a couple different setup.py files just to avoid duplicating version
information. But, copy-pasting is dumb and unit testing setup.py files is hard.
This code got factored out into vcversioner.
7259f58f0e