如果二维列表的元素不在范围内，如何处理错误

Question

我正在尝试错误处理 doughnuts_gone 的输入。用户应输入列表的元素位置。例如，如果他们想以 18 美元的价格删除 6 个奶油甜甜圈的订单，那么您应该输入列表的位置；先列出so位置0，然后把2d列表中的列表元素位置去掉。我的程序的问题是，如果输入的数字不在列表中可用元素的范围内，我不知道如何编写 elif 语句：elif i != total_order[i]:简化程序：def check_valid(prompt):        while True:            try:                i = int(input(prompt))                if i == '':                    print("You must enter a value for the doughnut item you would like to change.")                    print()                elif i != total_order[i]:                    print("Invalid")                else:                    break            except:                break        return itotal_order = [['Cream',6,18], ['Cookies',5,20], ['Jam',6,16]]for i in range(len(total_order)):    print("{}     {} {} Doughnuts = ${:.2f}".format(i, total_order[i][1],total_order[i][0],total_order[i][2]))doughnuts_gone = check_valid("Enter the number associated with the doughnut order you would like to remove? ")谢谢你！我希望这是有道理的！:)

Answer 1

您将i变量检查为字符串 ( if i == '':)，但它在前一行 ( i = int(input(prompt))) 中被强制转换为整数。您应该检查列表的长度而不是这一行：elif i != total_order[i]:。由于这个问题，您的脚本无法正常工作。我写了一个工作代码，我已经测试了它。请参阅下面我的代码/测试。

此外，您的货车会改进您的代码（例如：检查输入是否可以转换为整数。）。

代码：

def check_valid(prompt):

    while True:

        try:

            i = input(prompt)

            if not i:

                print("You must enter a value for the doughnut item you would like to change.")

                print()

            elif int(i) > len(total_order)-1:

                print("Invalid")

            else:

                break

        except:

            break

    return int(i)

total_order = [['Cream', 6, 18], ['Cookies', 5, 20], ['Jam', 6, 16]]

for i in range(len(total_order)):

    print("{}     {} {} Doughnuts = ${:.2f}".format(i, total_order[i][1], total_order[i][0],

                                                    total_order[i][2]))

doughnuts_gone = check_valid(

    "Enter the number associated with the doughnut order you would like to remove? ")

print("Valid value! Selected one: {}".format(total_order[doughnuts_gone]))

输出：

>>> python3 test.py

0     6 Cream Doughnuts = $18.00

1     5 Cookies Doughnuts = $20.00

2     6 Jam Doughnuts = $16.00

Enter the number associated with the doughnut order you would like to remove? 3

Invalid

Enter the number associated with the doughnut order you would like to remove? 

You must enter a value for the doughnut item you would like to change.

Enter the number associated with the doughnut order you would like to remove? 0

Valid value! Selected one: ['Cream', 6, 18]