```
class Foo1(dict):
    def __getattr__(self, key): return self[key]
    def __setattr__(self, key, value): self[key] = value

class Foo2(dict):
    __getattr__ = dict.__getitem__
    __setattr__ = dict.__setitem__

o1 = Foo1()
o1.x = 42
print(o1, o1.x)

o2 = Foo2()
o2.x = 42
print(o2, o2.x)
```

With CPython 2.5, 2.6 (similarly in 3.2), I get:
({'x': 42}, 42)
({}, 42)

With PyPy 1.5.0, I get the expected output::
({'x': 42}, 42)
({'x': 42}, 42)

I asked this also on SO: http://stackoverflow.com/questions/6305267/python-inconsistence-in-the-way-you-define-the-function-setattr

From the answers, I am not exactly sure wether this is considered as a bug in CPython or not. Anyway, I just wanted to post this here.

It's a CPython bug.

New changeset 971865f12377 by Benjamin Peterson in branch '3.2':
don't use a slot wrapper from a different special method (closes #14658)
http://hg.python.org/cpython/rev/971865f12377

New changeset 0c1c8f8955d8 by Benjamin Peterson in branch 'default':
merge 3.2 (#14658)
http://hg.python.org/cpython/rev/0c1c8f8955d8

New changeset e3eda2d91e93 by Benjamin Peterson in branch '2.7':
don't use a slot wrapper from a different special method (closes #14658)
http://hg.python.org/cpython/rev/e3eda2d91e93