def _add_to_topic_subscribed(self, topic, lport_id):
        if not self.enable_selective_topo_dist:
            return

        if self.topic_subscribed not in topic:
            LOG.info(_LI("Subscribe topic: %(topic)s by lport: %(id)s") %
                     {"topic": topic, "id": lport_id})
            self.nb_api.subscriber.register_topic(topic)
            self._pull_tenant_topology_from_db(topic, lport_id)
            self.topic_subscribed[topic] = set([lport_id])
        else:
            self.topic_subscribed[topic].add(lport_id)
dataset/ETHPy150Open openstack/dragonflow/dragonflow/controller/topology.py/Topology._add_to_topic_subscribed/swapped operands of `not in`