Alternative: Make Python dictionaries accessible as attributes

I saw @ yutaka2487's "Allow Python dictionary to be accessed as an attribute" and it seemed that it could be done by another method, so I tried it. I tried it. It's a simple way to turn the dictionary itself (self) into an attribute dictionary (__dict__). All the tests were ok, but if you have any pitfalls, please comment.

attrdict.py

class attrdict(dict):
    '''A dictionary that can also access attributes using its keyword.

    >>> ad = attrdict(a=1, b=2)
    >>> sorted(ad.items())
    [('a', 1), ('b', 2)]
    >>> ad['a'], ad.a
    (1, 1)
    >>> ad['b'], ad.b
    (2, 2)
    >>> ad['a'] = 3
    >>> ad['a'], ad.a
    (3, 3)
    >>> ad.b = 4
    >>> ad['b'], ad.b
    (4, 4)
    >>> ad['c'] = 5
    >>> ad['c'], ad.c
    (5, 5)
    >>> ad.d = 6
    >>> ad['d'], ad.d
    (6, 6)
    >>> sorted(ad.items())
    [('a', 3), ('b', 4), ('c', 5), ('d', 6)]
    '''

    def __init__(self, *args, **kwargs):
        dict.__init__(self, *args, **kwargs)
        self.__dict__ = self

if __name__ == '__main__':
    import doctest
    doctest.testmod()

test results

$ python attrdict.py -v
Trying:
    ad = attrdict(a=1, b=2)
Expecting nothing
ok
Trying:
    sorted(ad.items())
Expecting:
    [('a', 1), ('b', 2)]
ok
Trying:
    ad['a'], ad.a
Expecting:
    (1, 1)
ok
Trying:
    ad['b'], ad.b
Expecting:
    (2, 2)
ok
Trying:
    ad['a'] = 3
Expecting nothing
ok
Trying:
    ad['a'], ad.a
Expecting:
    (3, 3)
ok
Trying:
    ad.b = 4
Expecting nothing
ok
Trying:
    ad['b'], ad.b
Expecting:
    (4, 4)
ok
Trying:
    ad['c'] = 5
Expecting nothing
ok
Trying:
    ad['c'], ad.c
Expecting:
    (5, 5)
ok
Trying:
    ad.d = 6
Expecting nothing
ok
Trying:
    ad['d'], ad.d
Expecting:
    (6, 6)
ok
Trying:
    sorted(ad.items())
Expecting:
    [('a', 3), ('b', 4), ('c', 5), ('d', 6)]
ok
2 items had no tests:
    __main__
    __main__.attrdict.__init__
1 items passed all tests:
  13 tests in __main__.attrdict
13 tests in 3 items.
13 passed and 0 failed.
Test passed.