Python 如何用大写字母阻止崩溃

有没有办法阻止此代码中的字符（字母）：

x = '6'
while x != '5':

    try:
        a = int(input('please enter what the first digit should be = '))
        b = int(input('please enter what the second digit should be = '))
        op = input('press 1 to add, 2 to subtract, 3 to multiply or 4 to divide:')
        if op == '1':
            c = a + b
        elif op == '2':
            c = a - b
        elif op == '3':
            c = a * b
        elif op == '4':
            if b == 0:
                c = 'cannot divide by 0'
            else:
                c = a / b
        else:
            c = 'a error'

        print('Your answer is = ',c)

    except ValueError:
        print('Something went wrong! Please ensure you only entered numbers!!')


    x = input('Press 5 to exit or 6 to continue: ')
    if x != '5':
        print('We continue :) ')
    else:
        print("Sad to see you go. Bye!")

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我正在制作一个计算器应用程序，我想通过阻止所有字母来阻止崩溃。

请在您的问题中包含完整的错误消息。可能重复您所说的阻止是什么意思？是否希望在键入字符（字母）后仍运行循环？还是要停止执行并引发异常？