code: def subscribe(self, connection, destination):
          
          self.log.debug("Subscribing %s to %s" % (connection, destination))
          self._topics[destination].add(connection)
docs: Subscribes a connection to the specified topic destination. 
  
          @param connection: The client connection to subscribe.
          @type connection: L{coilmq.server.StompConnection}
  
          @param destination: The topic destination (e.g. '/topic/foo')
          @type destination: C{str}