def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def __init__(self, m1, m2):
        super(differencematcher, self).__init__(m1._root, m1._cwd)
        self._m1 = m1
        self._m2 = m2
        self.bad = m1.bad
        self.traversedir = m1.traversedir