For modules imported from CPython stdlib, I saw far just set version as 1.0, and then added/incremented micro version if any tweaks were later required.
But I guess, it would be more informative to set version to CPython's version from which module was imported, and then probably add revision suffix for any changes, e.g. "3.3.3-1". Hyphen in revision suffix of course assumed PyPI is ok with it (needs testing).
Comments welcome.