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 encode(self):
        if self.version == 6:
            return {'ip6': self.ip_addr}
        else:
            return {'ip4': self.ip_addr}