Well, now every attr access goes thru __getattr__-method, so this could cause situations which give not so clear diagnostics:
Please update to 2.2a4. Every new-style instance attribute access goes throuh __getattribute__; __getattr__ does the same as for classic classes.
It's true that if you screw with __getattribute__, you'll still break your objects; but that's hard to avoid given how things work.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)