Question

当用户输入无效值存储到“数字”变量时，我无法保护脚本不会崩溃。

程序的目的：允许用户输入整数，将它们存储到列表中，然后查找并打印最高编号。输入中不允许使用字符串或浮点数。

功能

getNum(prompt) - 测试并将输入的值转换为整数并返回y。
swap(A, x, y) - 用于对数据进行排序的简单交换例程函数。（目前尚未使用）
sortNum(A) - 排序并使用列表中的Swap例程。
maxIt(numbers) - 查找列表中的最高编号。（使用中），如果我使用这个最大功能，我认为我甚至不需要对列表进行排序。
main()

代码：

def getNum(prompt):
    # Function to call when asking for the numbers later.
    # Try/except to catch crashes if failing to store integer.
    try:
        x = input(prompt)
        y = int(x)
        return y

    # Message to print when excepting.
    except:
        print("I was expecting an integer number, please try again... \n")


# Function to swap to highest # in list 'numbers'.
def swap(A, x, y):
    temp1 = A[x]
    A[x] = A[y]
    A[y] = temp1

# Function to perform the looping/swap routine.
# Program can find max with separate function.
## This function is to sort the numbers in the list.
def sortNum(A):
    for i in range(len(A)):
        for k in range(len(A) - 1):
            first = k
            second = k + 1

            if (A[first] > A[second]):
                # Uses Swap function
                swap(A, first, second)

# Function to find the highest number in the list.
def maxIt(numbers):
    maxNum = numbers[0]
    for i in numbers:
        if i > maxNum:
            maxNum = i
    return maxNum

# Start main
def main():

    # Creates the numbers array.
    numbers = []

    # Starts the loop to enter numbers into the array.
    done = False
    while not done:
        numInput = getNum("Please enter an integer or < 0 to finish >: ")

        # Stores every input from numInput into numbers.
        numbers.append(numInput)

        #  Test condition to break out of loop '0'.
        if numInput is 0:

            # Prints the resulting max number once finished.
            print("The maximum value is: " + str(maxIt(numbers)))

            # Flag to stop the program once finished.
            done = True

main()

当getNum的测试没有失败时的当前输出（str或float）：

Please enter an integer or < 0 to finish >: 222
Please enter an integer or < 0 to finish >: 333
Please enter an integer or < 0 to finish >: 444
Please enter an integer or < 0 to finish >: 555
Please enter an integer or < 0 to finish >: 666
Please enter an integer or < 0 to finish >: 777
Please enter an integer or < 0 to finish >: 888
Please enter an integer or < 0 to finish >: 999
Please enter an integer or < 0 to finish >: 0
The maximum value is: 999

将str或float输入getNum / numInput：

Please enter an integer or < 0 to finish >: 222
Please enter an integer or < 0 to finish >: 333
Please enter an integer or < 0 to finish >: 444
Please enter an integer or < 0 to finish >: test
I was expecting an integer number, please try again...

Please enter an integer or < 0 to finish >: 555
Please enter an integer or < 0 to finish >: 666
Please enter an integer or < 0 to finish >: 0
Traceback (most recent call last):
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 64, in <module>
    main()
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 59, in main
    print("The maximum value is: " + str(maxIt(numbers)))
  File "C:\Users\Bar\Desktop\IS115\Peretz_A9.py", line 37, in maxIt
    if i > maxNum:
TypeError: '>' not supported between instances of 'NoneType' and 'int'

Answer 1

好吧，问题是你的函数getNum在数字无效时返回None，请尝试以下方法进行快速修复：

if numInput is not None:
    numbers.append(numInput)

但我也建议您阅读：

Why is "except: pass" a bad programming practice?

并尝试避免代码中的空except子句！

Answer 2

问题是你的try..except在特殊情况下没有返回任何内容（返回None）：

def getNum(prompt):
    # Function to call when asking for the numbers later.
    # Try/except to catch crashes if failing to store integer.
    try:
        x = input(prompt)
        y = int(x)
        return y

    # Message to print when excepting.
    except:
        print("I was expecting an integer number, please try again... \n")
        # Returns None resulting in your error

您可以通过将输入置于循环中来避免这种情况：

def getNum(prompt):
    # Function to call when asking for the numbers later.
    # Try/except to catch crashes if failing to store integer.
    while True:
        try:
            x = input(prompt)
            y = int(x)
            return y

        # Message to print when excepting.
        except ValueError:
            print("I was expecting an integer number, please try again... \n")

Answer 3

问题位于函数getNum中。实际上，当您在输入中键入一些文本时，函数getNum会出现异常，因为您尝试将非数字str强制转换为int，然后打印消息并且函数返回...... None。 None存储在numInput中，然后添加到列表中。你知道接下来的事情。

为了使这项工作，你应该测试getNum的输出。

Answer 4

您的getNum返回int或None（打印消息后）。 main即使无，也无条件地附加返回值。因此比较信息。变化

    numbers.append(numInput)

到

    if isinstance(numInput, int):
        numbers.append(numInput)

在没有max（）

4 个答案: