docs: def create_subscriber(self):
          '''Create a subscriber instance using specified addresses and
          message types.
          '''
          if self.subscriber is None:
              if self.topics:
                  self.subscriber = NSSubscriber(self.services, self.topics,
                                                 addr_listener=True,
                                                 addresses=self.addresses,
                                                 nameserver=self.nameserver)
                  self.recv = self.subscriber.start().recv