如果二维列表的元素不在范围内，如何处理错误答案

【问题标题】：How to error handle if the element of the 2d list is not within range如果二维列表的元素不在范围内，如何处理错误
【发布时间】：2020-07-03 10:23:39
【问题描述】：

我试图错误处理 donuts_gone 的输入。用户应输入列表的元素位置。例如，如果他们想删除 18 美元的 6 个奶油甜甜圈的订单，那么您应该输入列表的位置；首先列出位置0，然后删除2d列表中的列表元素位置。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 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? ")

谢谢！我希望这是有道理的！ :)

【问题讨论】：

标签： python list function error-handling

【解决方案1】：

您将 i 变量作为字符串 (if i == '':) 进行了检查，但在前一行 (i = int(input(prompt))) 中将其转换为整数。您应该检查列表的长度而不是这一行：elif i != total_order[i]:。由于此问题，您的脚本无法正常工作。我已经编写了一个工作代码并对其进行了测试。请看下面我的代码/测试。

此外，您的面包车改进了您的代码（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]

【讨论】：