Reading What's New in Python 2.2 I see they are changing integer division which sounds broke
I've got 3 Python versions at home, 4 at work. What a compatibility nightmare.
Found the issue with __debug__ I had in this thread on python dev: assignments to __debug__ are disallowed although it doesn't seem to be in the python changes document.
Guido says: "To enforce a restriction that was always intended: __debug__ should be a read-only variable."