code: def cancel_order(self, order_id, acc_id=0):
          
          ret, data = self._trade_ctx.modify_order(ft.ModifyOrderOp.CANCEL, order_id=order_id, qty=0, price=0,
                                                   adjust_limit=0, trd_env=self._env_type, acc_id=acc_id)
  
          # ret不为0时， data为错误字符串
          if ret == ft.RET_OK:
              return ret, ''
          else:
              return ret, data
docs: 取消订单