Currying dictionary assignment in Python

curriedgetitem.py

class ProxiedGetitem(object):
    """Dictionary whose keys are 2-element tuples; if one element tuple used,
    the __getitem__ method is curried

    >>> d = ProxiedGetitem()
    >>> d # doctest: +ELLIPSIS
    <__main__.ProxiedGetitem object at 0x...>
    >>> d[1,2] = 'a'
    >>> d[1,2]
    'a'
    >>> d[1] # doctest: +ELLIPSIS
    <"Curried" getitem object for <__main__.ProxiedGetitem object at 0x...>>
    >>> d[1][2]
    'a'
    >>> d[1][2] = 'b'
    >>> d[1,2]
    'b'
    """

    def __init__(self):
        self.d = {}

    def __getitem__(self, key):
        if isinstance(key, tuple) and len(key) == 2:
            return self.d[key]
        else:
            return CurriedGetitem(self, key)

    def __setitem__(self, key, value):
        if isinstance(key, tuple) and len(key) == 2:
            self.d[key] = value
        else:
            raise KeyError

class CurriedGetitem(object):

    def __init__(self, parent, index):
        self.parent = parent
        self.first_index = index

    def __repr__(self):
        return '<"Curried" getitem object for '+repr(self.parent)+'>'

    def __getitem__(self, key):
        return self.parent[(self.first_index, key)]

    def __setitem__(self, key, value):
        self.parent[(self.first_index, key)] = value

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