Python 3 中的 Else 语句始终运行 [英] Else statement in Python 3 always runs

问题描述

我一直在用 Python 制作一个基本的计算器，但我遇到了这个问题.计算完成后，总是打印无效数字"，然后暂停.我认为这与打破 if 块的换行符有关，但我不确定.

I've been making a basic calculator with Python and I have come across this issue. After the calculations are made "Invalid Number" always prints and then the pause happens. I think it has something to do with the newline breaking the if block but I'm not sure.

任何帮助将不胜感激.提前致谢.

Any help will be appreciated. Thanks in advance.

def badnum():
        print("Invalid Number")
        print("Press enter to continue")
        input("")
def main():
        print("Select an action ")
        print("1.) Add")
        print("2.) Subtract")
        print("3.) Multiply")
        print("4.) Divide")
        ac = int(input(">>>"))
        if ac == 1:
                print("First number :")
                fn = float(input(">>>"))
                print("Second number :")
                sn = float(input(">>>"))
                a = fn+sn
                print(a)
        if ac == 2:
                print("First number :")
                fn = float(input(">>>"))
                print("Second number :")
                sn = float(input(">>>"))
                a = fn-sn
                print(a)
        if ac == 3:
                print("First number :")
                fn = float(input(">>>"))
                print("Second number :")
                sn = float(input(">>>"))
                a = fn*sn
            print(a)
        if ac == 4:
                print("First number :")
                fn = float(input(">>>"))
                print("Second number :")
                sn = float(input(">>>"))
                a = fn/sn
                print(a)
        else:
                badnum()
print("
"*100)
while True:
    try:
        main()
    except ValueError:
        badnum()
    except ZeroDivisionError:
        print("Infinity")
    print("
"*100)

推荐答案

不，这与您编写代码的方式有关，请考虑使用 if...elif:

No, it has got something to do with how you have written your code, consider this with if...elif:

ac = int(input(">>>"))
if ac == 1:
        print("First number :")
        fn = float(input(">>>"))
        print("Second number :")
        sn = float(input(">>>"))
        a = fn+sn
        print(a)
elif ac == 2:
        print("First number :")
        fn = float(input(">>>"))
        print("Second number :")
        sn = float(input(">>>"))
        a = fn-sn
        print(a)
elif ac == 3:
        print("First number :")
        fn = float(input(">>>"))
        print("Second number :")
        sn = float(input(">>>"))
        a = fn*sn
        print(a)
elif ac == 4:
        print("First number :")
        fn = float(input(">>>"))
        print("Second number :")
        sn = float(input(">>>"))
        a = fn/sn
        print(a)
else:
        badnum()

<小时>解释:之前，您正在检查 ac == 1 和 ac == 4 不能同时为真，所以第二个 else 语句也被执行了.这可以通过 if..elif 结构省略:一旦较早的比较之一变为真，其余的就不再执行.

---

Explanation: Before, you were checking for ac == 1 and ac == 4 which cannot both be true, so the second else statement was executed as well. This can be omitted with the if..elif construction: once, one of the earlier comparisons become true, the rest is not executed anymore.

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