code: def maturity_date(self):
          
          try:
              return self.__dict__["maturity_date"]
          except (KeyError, ValueError):
              raise AttributeError(
                  "Instrument(order_book_id={}) has no attribute 'maturity_date' ".format(self.order_book_id)
              )
docs: [datetime] 期货到期日。主力连续合约与指数连续合约都为 datetime(2999, 12, 31)（期货专用）