code: def _GetSerializedAttributeContainerList(self, container_type):
      
      container_list = self._serialized_attribute_containers.get(
          container_type, None)
      if not container_list:
        container_list = SerializedAttributeContainerList()
        self._serialized_attribute_containers[container_type] = container_list
  
      return container_list
docs: Retrieves a serialized attribute container list.
  
      Args:
        container_type (str): attribute container type.
  
      Returns:
        SerializedAttributeContainerList: serialized attribute container list.