code: def settlement_method(self):
          
          try:
              return self.__dict__["settlement_method"]
          except (KeyError, ValueError):
              raise AttributeError(
                  "Instrument(order_book_id={}) has no attribute 'settlement_method' ".format(self.order_book_id)
              )
docs: [str] 交割方式，’CashSettlementRequired’ - 现金交割, ‘PhysicalSettlementRequired’ - 实物交割（期货专用）