code: def shutdown(self):
          
          with self._lock:
              if self.is_shutdown:
                  return
              else:
                  self.is_shutdown = True
  
          if self._idle_heartbeat:
              self._idle_heartbeat.stop()
  
          self.scheduler.shutdown()
  
          self.control_connection.shutdown()
  
          for session in tuple(self.sessions):
              session.shutdown()
  
          self.executor.shutdown()
  
          _discard_cluster_shutdown(self)
docs: Closes all sessions and connection associated with this Cluster.
          To ensure all connections are properly closed, **you should always
          call shutdown() on a Cluster instance when you are done with it**.
  
          Once shutdown, a Cluster should not be used for any purpose.