为什么在用户要求重新启动程序后不重置代码？

Question

So this is my code. Upgraded. I had some issues with the While loops but I ve managed to get over it. Now my problem is this. When the user gets at the end of the loop and is being asked to play again the program won t change its random number. Any help would be really appreciated. And as the title says, python won t recognize capital Y and N and it will only take y and n.

from random import *
def play():
    return guess()

def retry():
    while True:
        replay = input("Try again ?(Y/N)")
        if replay not in {"y", "n"}:
            print("Please enter Yes or No")
        elif replay.lower() == "n":
            print("Thanks for playing! Bye now!.")
            break
        elif replay.lower() == "y":
            print("As you wish!")
            return guess()

def guess():
    while True:
        user = int(input("Guess the number: \n"))
        print(user,a)
        if user < a:
            print("Higher")
        elif user > a:
            print("Lower")
        if user == a:
            return retry()
a = randint(0,20)



play()

Answer 1

It doesn't reset a because it was never instructed to do so. When you restart the game, you should generate a new number:

...
        elif replay.lower() == "y":
            print("As you wish!")

            # Tell the interpreter that we want to modify a variable from the global scope
            global a

            # Generate a new random number
            a = randint(0,20)

            return guess()

...

And as the title says, python won t recognize capital Y and N and it will only take y and n

You should change the following line:

        replay = input("Try again ?(Y/N)")

To:

        replay = input("Try again ?(Y/N)").lower()

Otherwise your following condition will fail, because Y and N are not in {"y", "n"} . Though, the brackets doesn't really make sense here, and would be better to simply do:

if replay not in "yn":

EDIT: Instead of validating the answer twice, just look for valid answers and then ask for a valid one if it wasn't provided:

replay = input("Try again ?(Y/N)").lower()
if replay == 'y':
    # replay...
elif replay = 'n'
    print("Thanks for playing! Bye now!.")
    break
else:
    print("Please enter Yes or No")

EDIT: To ensure the given input is a valid number, you could use a try/except block to catch the error:

try:
    user = int(input("Guess the number: \n"))
except ValueError:
    print('Not a valid number.')

Or you could ensure the given string is a number using str.isdigit :

user = input("Guess the number: \n")
if user.isdigit():
    user = int(user)
else:
    print('Not a valid number.')

I would personally go with the try/except since the second is basically validating the string twice (once through isdigit , then another when the int cast is done).