I am trying to program a Streets and Alleys card game with Python and I'm having some trouble handling when a function returns None. Essentially, my program prompts the menu of choices, then another line calling a function which is get_option. When the get_option is returned, it is returned as a list and the list could be either a single character long (U, R, H, Q), it could be 1 string and 2 ints (MTF 5 2) or just return None. In my main, I'm having trouble trying to restart my original while loop which contains the get_option function being called. If what I'm asking doesn't make sense, let me know and I can try to explain it more in depth. Here is my code:

def get_option():
    '''Prints option menu and takes
    user input to determine which 
    option will follow'''
    while True:
        
        option = str(input("\nInput an option (MTT,MTF,MFT,U,R,H,Q): ")).lower()
        
        option_list = option.split()
        
        mxx = ["MTT", "MTF", "MFT"]
        
        for item in option_list:
            mode = str(item[0])
            for c in mode:
                if c == "u":
                    option_list[0] = c.upper()
                    return option_list
                
                if c == "r":
                    option_list[0] = c.upper()
                    return option_list
                
                if c == "h":
                    option_list[0] = c.upper()
                    return option_list
                
                if c == "q":
                    option_list[0] = c.upper()
                    return option_list
                
                else:
                    print("Error in option:", option_list[0])
                    return None
                break
                
            if mode not in mxx:
                return None
            else:
                return option_list
            
            source = int(item[1])
            if 7 > source > 0:
                print("Error in Source.")
                return None
            else:
                return option_list
            
            destination = int(item[2])
            if 3 > destination > 0:
                print("Error in Destination")
                return None
            else:
                return option_list
         
def main():  

    the_deck = cards.Deck()  
    print("\nWelcome to Streets and Alleys Solitaire.\n")
    the_deck.shuffle()
    the_deck.display()
    
    print(MENU)

    while True:
        option_list = get_option()
        
        while True:
            if option_list == None:
                option_list = get_option()
                break
            else:
                break
            
        if "U" in option_list:
            print("Undo:")
            continue
            
        if "R" in option_list:
            print("\n- - - - New Game. - - - -\n")
            the_deck.shuffle()
            the_deck.display()
            continue
            
        if "H" in option_list:
            print(MENU)
            continue
        
        if "Q" in option_list:
            break
            
    print("Thank you for playing.")

if __name__ == '__main__':
     main()

CodePudding user response：

If you use a return statement inside a function, it will automatically break out of the function. If you need your function to continue to run you could try using a generator function or change your code so your while loop runs outside your function.

CodePudding user response：

You shouldn't break in both the if and else branches of in the while loop. You need to repeat the loop until you get a result that isn't None, and that's when you should break out.

def main():  

    the_deck = cards.Deck()  
    print("\nWelcome to Streets and Alleys Solitaire.\n")
    the_deck.shuffle()
    the_deck.display()
    
    print(MENU)

    while True:
        
        while True:
            option_list = get_option()
            if option_list is not None:
                break
            
        if "U" in option_list:
            print("Undo:")
            continue
            
        if "R" in option_list:
            print("\n- - - - New Game. - - - -\n")
            the_deck.shuffle()
            the_deck.display()
            continue
            
        if "H" in option_list:
            print(MENU)
            continue
        
        if "Q" in option_list:
            break
            
    print("Thank you for playing.")