如何从 if 语句内部 return 到程序开头？

Question

我正在练习一些基本的编码，我是运行一个简单的数学程序运行在终端上的 Visual Studio 代码。

如何在程序开头创建 return 选项，或者在陷入 if 语句后退出程序？

示例：

#beginning of program

user_input=input('Please select "this" or "that": ')
findings=user_input

If findings == this:
        print(this)
        # How can I redirect back to first user input question, instead 
        # of just ending here? 
if findings == that:
        print (that)
        # Again, How do I redirect back to first user input, instead of 
        # the program ending here?  
# Can I setup a Play_again here with options to return to user_input, 
        # or exit program? And then have all other If statements 
        # redirect here after completion? How would I do that? with 
        # another If? or with a for loop? 
#end program

Answer 1

您可以尝试将整个程序包装在一个 while 循环中，如下所示：

while(True):
    user_input=input('Please select "this" or "that": ')
    this = 'foo'
    if user_input == this:
        print(this)
        continue 

    if user_input == this:
        print(this)
        continue

Answer 2

不幸的是，'another technique' 我想使用它并没有奏效。

代码如下（修改第一个例子）：

import sys

def main():
    # Lots of setup code here.
    def start_over():
        return #Do nothing and continue from the next line
    condition = 1==1 #Just a sample condition, replace it with "check(condition)".
    float_condition = condition

    def play(*just_define:bool):
        if not just_define:
            play_again = input('play again? "y" or "n"')
    
            if play_again == 'y':
                start_over() #Jump to the beginning of the prohram.
            if play_again == 'n':
                sys.exit() #Exit the program
        
    while True:
        if float_condition == True:
            # print(float_condition)
            play() #skip to play_again from here?
    
        if float_condition == False:
            #print(float_condition)
            play() #skip to play_again from here?

    #I removed the extra "main()" which was here because it'd cause an infinite loop-like error.

main()

输出：

play again? "y" or "n"y
play again? "y" or "n"n

Process finished with exit code 0

play(*just_define:bool)函数中的*使just_define参数可选。如果您想 only 告诉 Python 搜索此函数，请使用该参数，这样它就不会抛出 ReferenceError 并且不会执行该行之后的任何内容if not just_define:。如何调用：play(just_define=True).

我用过nested functions。我已经 defined play 以便您可以从代码中的其他地方调用它。

Answer 3

感谢@Hack3r - 我终于能够选择 return 回到程序的开头或退出。但这导致了一个新问题。现在我的 print(results) 打印了 4 或 5 次...

这是我构建并正在使用的实际代码：

def main():

    math_Options=['Addition +','Subtraction -','Multiplication *','Division /']
    math_func=['+','-','*','/']
    for options in math_Options:
        print(options)
    print('Lets do some Math! What math function would you like to use? ')
   
    while True:
        my_Math_Function = input('Please make your choice from list above using the function symbol: ') 
        my_Number1=input('Please select your first number: ')
        x=float(my_Number1)
        print('Your 1st # is: ', x)
        my_Number2=input('Please select your Second Number: ')
        y=float(my_Number2)
        print('Your 2nd # is: ', y)
        z=float()
        print('')
        for Math_function in math_func:
            if my_Math_Function == math_func[0]:
                z=x+y
            if my_Math_Function == math_func[1]:
                z=x-y
            if my_Math_Function == math_func[2]:
                z=x*y
            if my_Math_Function == math_func[3]:
                z=x/y

            if (z % 2) == 0 and z>0:    
                print(z, ' Is an EVEN POSITIVE Number')
            if (z % 2) == 1 and z>0:    
                print(z, ' IS a ODD POSTIVE Number')
            if (z % 2) == 0 and z<0:
                print(z, ' Is an EVEN NEGATIVE Number')
            if (z % 2) ==1 and z<0:
                print(z, ' IS a ODD NEGATIVE Number')
            if z==0:
                print(z, 'Is is Equal to Zero')
            print('')
        play_again=input('Would you like to play again? "y" or "n" ')
        if play_again == 'y':
            continue
        if play_again == 'n':
            break
        main()
main()

如何从 if 语句内部 return 到程序开头？

How to return to beginning of program from inside of if statement?

for-loop

if-statement

return

exit

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