def underlying_symbol(self):
        """
        [str] 合约标的代码，目前除股指期货(IH, IF, IC)之外的期货合约，这一字段全部为’null’（期货专用）
        """
        try:
            return self.__dict__["underlying_symbol"]
        except (KeyError, ValueError):
            raise AttributeError(
                "Instrument(order_book_id={}) has no attribute 'underlying_symbol' ".format(self.order_book_id)
            )
def underlying_symbol ( self ) : try : return self . __dict__ [ "underlying_symbol" ] except ( KeyError , ValueError ) : raise AttributeError ( "Instrument(order_book_id={}) has no attribute 'underlying_symbol' " . format ( self . order_book_id ) )
[str] 合约标的代码，目前除股指期货(IH, IF, IC)之外的期货合约，这一字段全部为’null’（期货专用）