Calculates union between sets
            @others: one or several :class:RedisSet objects or #str redis set
                keynames

            -> #set of new set members

def union(self, *others):
        """ Calculates union between sets
            @others: one or several :class:RedisSet objects or #str redis set
                keynames

            -> #set of new set members
        """
        others = self._typesafe_others(others)
        return set(map(
            self._loads, self._client.sunion(self.key_prefix, *others)))