Python计算器：检查输入有效性

Question

我的代码看起来运行得很好，但就是没有打印出 except Exception: 下面的那句：print("这个输入无效。")。我尝试去修复它，但情况变得更糟。有没有人能帮我看看我缺少了什么？谢谢！

正确输出示例：

Calculator
Give a number: hah, NEVER
This input is invalid.
Give a number: What?
This input is invalid.
Give a number: 100
Give a number: Just kidding
This input is invalid.
Give a number: 50
(1) +
(2) -
(3) *
(4) /
(5)sin(number1/number2)
(6)cos(number1/number2)
(7)Change numbers
(8)Quit
Current numbers: 100 50
Please select something (1-6): 2
The result is: 50
(1) +
(2) -
(3) *
(4) /
(5)sin(number1/number2)
(6)cos(number1/number2)
(7)Change numbers
(8)Quit
Current numbers: 100 50
Please select something (1-6): 8
Thank you!

我的代码：

def getnumber():
    while True:
        try:
            number = input("Give a number: ")
            if number.isdigit():
                return number

        except Exception:
            print("This input is invalid.")

def main():
    import math
    print("Calculator")
    promptForNumbers = True

    while True:

        if promptForNumbers:


            number1 = int(getnumber())

            number2 = int(getnumber())

            promptForNumbers = False
        print("(1) +\n\n(2) -\n\n(3) *\n\n(4) /\n\n(5)sin(number1/number2)\n\n(6)cos(number1/number2)\n\n(7)Change numbers\n\n(8)Quit\n")
        print("Current numbers: %s %s" % (number1, number2))
        selection = int(input("Please select something (1-8): "))        


        if selection == 1:
            print("The result is: %s" % (number1 + number2))
            print("\n")
        elif selection == 2:
            print("The result is: %s" % (number1-number2))
            print("\n")
        elif selection==3:
            print("The result is: %s" % (number1*number2))
            print("\n")
        elif selection==4:
            print("The result is: %s" % (number1/number2))
            print("\n")
        elif selection==5:
            print("The result is: %s" % math.sin(number1/number2))
            print("\n")
        elif selection==6:
            print("The result is: %s" % math.cos(number1/number2))
            print("\n")
        elif selection==8:
            print("Thank you!")
            break
        elif selection==7:
            promptForNumbers = True
        else:
            print("Selection was not correct.")  
if __name__ == "__main__":
    main()

Answer 1

试试这个：

def getnumber():
    while True:
        number = raw_input("Give a number: ")

        if number.isdigit():
            return number
        else:
            print("This input is invalid.")

Answer 2

    if number.isdigit():
            return number

    else:

        raise ValueError('Not a valid input value.')

当然可以！请把你想要翻译的内容发给我，我会帮你把它变得简单易懂。

Answer 3

你没有看到异常语句被执行的原因，是因为在你的try块里面没有任何代码会引发异常。不过，如果你传给int构造函数的东西不是数字，它会引发一个ValueError异常。

根据我的理解，在这种情况下，尝试转换输入，然后捕获异常，是最符合Python风格的输入验证方式。你可以在这个链接中了解更多关于Python异常的内容。

def getnumber():
    while True:
        try:
            return int(input("Give a number: "))
        except ValueError:
            print("This input is invalid.")

你需要确保在main函数中调用getnumber的地方，去掉所有int的调用。另外，还有一点要注意，通常情况下，导入语句应该放在文件的最上面。如果你想了解更多，可以查看PEP8。