code: def get_queue_for(
              self,
              queue_identifier: QueueIdentifier,
      ) -> NotifyingQueue:
          
          queue = self.queueids_to_queues.get(queue_identifier)
  
          if queue is None:
              items: List[QueueItem_T] = list()
              queue = self.init_queue_for(queue_identifier, items)
  
          return queue
docs: Return the queue identified by the given queue identifier.
  
          If the queue doesn't exist it will be instantiated.