code: def next_id(self, channel):
          
  
          if channel not in self.topics:
              self.topics[channel] = 0
              return 0
  
          self.topics[channel] += 1
          return self.topics[channel]
docs: Get the next sequence number for a named channel or topic
  
          If channel has not been sent to next_id before, 0 is returned
          otherwise next_id returns the last id returned + 1.
  
          Args:
              channel (string): The name of the channel to get a sequential
                  id for.
  
          Returns:
              int: The next id for this channel