code: def start(self):
          
          if self._state == CLOSED:
              raise NSQException('producer already closed')
  
          if self.is_running:
              self.logger.warn('producer already started')
              return
  
          self.logger.debug('starting producer...')
          self._state = RUNNING
  
          for address in self.nsqd_tcp_addresses:
              address, port = address.split(':')
              self.connect_to_nsqd(address, int(port))
docs: Start discovering and listing to connections.