code: def sell(self, security, price=0, amount=0, volume=0, entrust_prop=0):
          
          return self._trade(security, price, amount, volume, "sell")
docs: 卖出股票
          :param security: 股票代码
          :param price: 卖出价格
          :param amount: 卖出股数
          :param volume: 卖出总金额 由 volume / price 取整， 若指定 price 则此参数无效
          :param entrust_prop: