I find it more convenient to access dict keys as obj.foo instead of obj[\'foo\'], so I wrote this snippet:
class AttributeDict(dict
From This other SO question there's a great implementation example that simplifies your existing code. How about:
class AttributeDict(dict):
__slots__ = ()
__getattr__ = dict.__getitem__
__setattr__ = dict.__setitem__
Much more concise and doesn't leave any room for extra cruft getting into your __getattr__ and __setattr__ functions in the future.