Victor> PyPy (and other Python implementations?) don't support non-string in type dictionary.
INADA Naoki> Wow! I thought it's Python's language. If we can prohibit non string name in all namespace, there might be possible optimization.

That's a different topic :-) It would be a backward incompatible change. Well... I don't think that anyone relies on this strange feature :-) IMHO it's more a side effect of the implementation, not a deliberate feature.