判断合约是否过期

def is_de_listed(self):
        """
        判断合约是否过期
        """
        instrument = Environment.get_instance().get_instrument(self._order_book_id)
        current_date = Environment.get_instance().trading_dt
        if instrument.de_listed_date is not None and current_date >= instrument.de_listed_date:
            return True
        return False