code: def is_de_listed(self):
          
          env = Environment.get_instance()
          instrument = env.get_instrument(self._order_book_id)
          current_date = env.trading_dt
  
          if instrument.de_listed_date is not None:
              if instrument.de_listed_date.date() > env.config.base.end_date:
                  return False
              if current_date >= env.data_proxy.get_previous_trading_date(instrument.de_listed_date):
                  return True
          return False
docs: 判断合约是否过期