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, test, nh, pmtu, table_id=0):
        self._test = test
        self.nh = nh
        self.pmtu = pmtu
        self.table_id = table_id