overloading __getattr__ and inheriting from dict

[Benoît Dejean]

class TargetWrapper(dict):

    def __init__(self, **kwargs):
        dict.__init__(self, kwargs)

    __getattr__ = dict.__getitem__
    __setattr__ = dict.__setitem__
    __delattr__ = dict.__delitem__



then 

tw = TargetWrapper()
tw.a = "spam" # ok
del tw.a # ok
tw.b = "egg"
print tw.b

last line give me an
AttributeError: 'TargetWrapper' object has no attribute 'b'

if i define

    def __getitem__(self, name):
        return dict.__getitem__(self, name)

    __getattr__ = __getitem__

then the accessing the b attribute is ok. what's wrong ?