code: def set_empty_region(self, region_id, type_id, generated_at,
                           error_if_entries_present=True):
          
          key = '%s_%s' % (region_id, type_id)
          if error_if_entries_present and self._history.has_key(key):
              raise ItemAlreadyPresentError(
                  "Orders already exist for the given region and type ID. "
                  "Pass error_if_orders_present=False to disable this failsafe, "
                  "if desired."
              )
  
          self._history[key] = HistoryItemsInRegionList(
              region_id, type_id, generated_at)
docs: Prepares for the given region+item combo by instantiating a
          :py:class:`HistoryItemsInRegionList` instance, which will track
          region ID, type ID, and generated time. This is mostly used for
          the JSON deserialization process in case there are no orders for
          the given region+item combo.
  
          :param int region_id: The region ID.
          :param int type_id: The item's type ID.
          :param datetime.datetime generated_at: The time that the order set
              was generated.
          :keyword bool error_if_entries_present: If True, raise an exception if
              an entry already exists for this item+region combo when this is
              called. This failsafe may be disabled by passing False here.