[BangPypers] Python moratorium

[Sidharth Kuruvila]

This is to allow the alternate implementations to catch up, and not
really about the users of the python language. Adding breaking changes
between versions of python 3 would just be bad language design, so
users should be fine either way.

I've found myself quite happy using many of the new features that were
added to python over the years. I'll certainly miss that.