code: def _PrepareForNextContainerType(self):
      
      self._active_container_type = self._container_types.pop(0)
  
      self._add_active_container_method = self._add_container_type_methods.get(
          self._active_container_type)
  
      query = 'SELECT _identifier, _data FROM {0:s}'.format(
          self._active_container_type)
      self._cursor.execute(query)
  
      self._active_cursor = self._cursor
docs: Prepares for the next container type.
  
      This method prepares the task storage for merging the next container type.
      It set the active container type, its add method and active cursor
      accordingly.