While循环即使是错误也停止了吗？

Question

I thought the logic of my while loop made sense, but it abruptly stops after the first loop.

choice=int(input("Enter choice:"))
if (choice=="" or (choice!=0 and choice!=1 and choice!=2)):
    valid = False
while valid == False:
    print("Invalid choice, please enter again")
    choice=int(input("Enter choice:"))
    return choice        
if choice ==1:
    valid=True
    display_modules_average_scores()
    menu()
elif choice ==2:
    valid=True
    display_modules_top_scorer()
    menu()
elif choice==0:
    exist=True
    print("===============================================")
    print("Thank you for using Students' Result System")
    print("===============================================")

If I enter 5, it does:

print("Invalid choice, please enter again")
choice=int(input("Enter choice:"))

But if I enter 5 again, it stops the program. What am I doing wrong?

Answer 1

if I enter 5 again, it stops the program

Because you have a return statement that immediate ends the function you're running within.

You seem to be trying to create an infinite loop. You can start with testing exit and invalid conditions with this. Note:choice will never equal an empty string

while True:
    choice=int(input("Enter choice (0 to exit):"))
    if choice == 1:
        pass # do something 
    elif choice == 2:
        pass # do something else 
    elif choice == 0:
        break
    else:
        print("Invalid choice, please enter again")
print("Thanks") 

To exit the loop, you can use break , which executes code after the loop. Use return to end the function, as mentioned. There is a difference

If you're running this loop inside of the menu() function, you do not need to actually call the menu function again. That's the point of the while loop

Answer 2

By defining the function we can perform this task easily with no code duplication. The Below code calls the function inputchoice() and then the inputchoice() will check the value entered by the user and if there the value is not valid then the inputchoice will call itself and the process continues untill the user enter correct input.

def inputchoice():
   choice=int(input("Enter choice: "))
   if (choice=="" or (choice!=0 and choice!=1 and choice!=2)):
       print("Invalid choice!")
       choice = inputchoice()
   return choice

def menu():
 choice = inputchoice()   
 print(choice)
 if choice ==1:
      valid=True
      print("Do something if Valid = True")
 elif choice ==2:
      valid=True
      print("Do something if Valid = True")
 elif choice==0:
      valid=True
      print("Do something if Valid = True")

menu()  #implementing menu function

Answer 3

I prefer making a dictionary with your functions, keeps the code clean in my eyes.

Consider this code here:

def choice1():
    return 'choice1'

def choice2():
    return 'choice2'

def defaultchoice():
    return 'default'

choicedict = {
    '1': choice1,
    '2': choice2
}

while True:
    choice = input("Enter choice (0 to exit):") # maintain as str to avoid error!
    if choice == '0':
        break
    value = choicedict.get(choice, defaultchoice)()
    print(value)

Answer 4

Single Function Code

def menu():
 choice=int(input("Enter choice:"))


 if (choice=="" or (choice!=0 and choice!=1 and choice!=2)):
    print("Invalid choice, please enter again")
    menu()
 elif choice ==1:
    print("Oh, its working")
    menu()
 elif choice ==2:
    print("Oh, its working")
    menu()
 elif choice==0:
    print("===============================================")
    print("Thank you for using Students' Result System")
    print("===============================================")

menu()

Answer 5

Hi i would use a while loop like this. It would seem from this assignment that we are from the same institution. This is what i use for my code, I hope this helps.

while True:
    user_input = input("Enter choice: ")
    if (user_input == "0"):
        print("=====================================================")
        print("Thank You for using Students' Result System")
        print("=====================================================")
        break
    elif(user_input == "1"):
        display_modules_average_scores()      

    elif(user_input == "2"):
        display_modules_top_scorer()
    else:
        print("Invalid choice, please enter again")