python – 错误：游标’对象没有属性’_last_executed

cursor.execute("SELECT price FROM Items WHERE itemID = ( 
                  SELECT item_id FROM Purchases 
                  WHERE purchaseID = %d AND customer_id = %d)",[self.purchaseID,self.customer])

我得到这个错误

'Cursor' object has no attribute '_last_executed'

但是当我尝试这个：

cursor.execute("SELECT price FROM Items WHERE itemID = ( 
                  SELECT item_id FROM Purchases 
                  WHERE purchaseID = 1 AND customer_id = 1)",)

没有错误.我该如何解决？