[str] 交割方式，’CashSettlementRequired’ - 现金交割, ‘PhysicalSettlementRequired’ - 实物交割（期货专用）

def settlement_method(self):
        """
        [str] 交割方式，’CashSettlementRequired’ - 现金交割, ‘PhysicalSettlementRequired’ - 实物交割（期货专用）
        """
        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)
            )