在Python中，可以停止来自另一个函数的循环吗？

Question

我想要一个程序，从主菜单开始，分支到不同的功能。在每个功能结束时，我希望用户被问到“你想回到主菜单吗？”如果用户说不，我希望程序通过停止主循环来终止（我不想使用系统出口（）或任何类似的东西）。 示例代码：

#Issue is almost at the bottom
#Feel free to comment on the rest of the code as well,
#Always looking to improve
def main():
    loop = True
    while loop:
        print('''MENU CHOICE''')
        print('''1: go here''')
        print('''2: go there''')
        print('''3: You get the point''')
        print('''0: Terminate program''')
        print()

        try:
            answer = int(input('''I want to go to program: '''))
        except:
            print('''Not a valid menu choice, please try again''')
            print()

        if answer != 1 and answer != 2 and answer != 3 and answer != 0:
            print('''Not a valid menu choice, please try again''')
            print()
        elif answer == 1:
            program1()
        elif answer == 2:
            program2()
        elif answer == 3:
            program3()
        else:
            loop = False

def program1():
    print('''This is program 1''')
    itdontwork = input('''Do you want to go back to the menu? Y/N''')

    if itdontwork == 'Y' or itdontwork == 'y':
        print()
    else:
        print('''SHUTTING DOWN''')
        loop = False #Here is the issue

#The rest of the programs would be the same

main()

Answer 1

最简单的方法是使变量循环全局化

loop = True
def main():
    global loop
    while loop:
        print('''MENU CHOICE''')
        print('''1: go here''')
        print('''2: go there''')
        print('''3: You get the point''')
        print('''0: Terminate program''')
        print()

        try:
            answer = int(input('''I want to go to program: '''))
        except:
            print('''Not a valid menu choice, please try again''')
            print()

        if answer != 1 and answer != 2 and answer != 3 and answer != 0:
            print('''Not a valid menu choice, please try again''')
            print()
        elif answer == 1:
            program1()
        elif answer == 2:
            program2()
        elif answer == 3:
            program3()
        else:
            loop = False

def program1():
    global loop
    print('''This is program 1''')
    itdontwork = input('''Do you want to go back to the menu? Y/N''')

    if itdontwork == 'Y' or itdontwork == 'y':
        print()
    else:
        print('''SHUTTING DOWN''')
        loop = False #Here is the issue

#The rest of the programs would be the same

main()

Global将允许您在任何地方都有相同的w/r变量。没有全局变量，所有变量都是局部变量。在

Answer 2

问题是您试图更改在program1函数范围之外定义的变量。loop是在main中定义的，因此只有main可以访问它。有几种方法可以解决这个问题，您可以在外部声明loop（使其成为一个全局的），或者让您的program1向调用函数返回一个布尔值，例如：

def main():
    loop = True
    while loop:
        loop = program1()

def program1():
    itdontwork = input('''Do you want to go back to the menu? Y/N''')
    if itdontwork == 'Y' or itdontwork == 'y':
        print()
    else:
        print('''SHUTTING DOWN''')
        return False

Answer 3

我想你想做的是让不同的程序返回一个值。在

问题是函数被执行但什么也不返回。你的main函数什么也不返回；因此循环变量永远不能被更新来中断循环。在

#Issue is almost at the bottom
#Feel free to comment on the rest of the code as well,
#Always looking to improve
def main():
    loop = True
    while loop:
        print('''MENU CHOICE''')
        print('''1: go here''')
        print('''2: go there''')
        print('''3: You get the point''')
        print('''0: Terminate program''')
        print()

        try:
            answer = int(input('''I want to go to program: '''))
        except:
            print('''Not a valid menu choice, please try again''')
            print()

        if answer != 1 and answer != 2 and answer != 3 and answer != 0:
            print('''Not a valid menu choice, please try again''')
            print()
        elif answer == 1:
            return program1() # Return the output of this function
        elif answer == 2:
            return program2() # Return the output of this function
        elif answer == 3:
            return program3() # Return the output of this function
        else:
            loop = False

def program1():
    print('''This is program 1''')
    itdontwork = input('''Do you want to go back to the menu? Y/N''')

    if itdontwork == 'Y' or itdontwork == 'y':
        print()
    else:
        print('''SHUTTING DOWN''')
        return False # Return the output of this function

#The rest of the programs would be the same

main()