> Oh, and "what to do of the now unused pure Python implementations in
io.py"?  Easiest would be to dump them, as they will probably get
hopelessly out of sync, but perhaps there's some genuine
portability/educational advantage to keep them?

The test suite should be run against both implementations.  That way
tested behavior will always be the same for both.  And all of its
behavior is tested, right? ;)

The value in the Python implementation is manifold.  For example:

  * It eases testing of new features/techniques.  Rather than going
straight to the C version when someone has an idea for a feature, it can
be implemented and tried out in Python.  If it's cool, then the extra
effort of porting to C can be undertaken.
  * It helps other Python implementations immensely.  PyPy, IronPython,
and Jython are all going to have to provide this library eventually (one
supposes).  Forcing them each to re-implement it will mean it will be
that much longer before they support it.