python - Where do I check for valid input in my rock paper scissors game

Question

I would like to check for valid input when the user inputs a choice between 'r', 'p', 's' How would I go about doing this? And where in my code do I put it?

I've already tried adding this in the beginning and it didn't work:

possible_choices = ["r", "p", "s"]

def play():
    user = input(
        "What's your choice? 'r' for rock, 'p' for paper, 's' for scissors: "
    ).lower
    computer = random.choice(["r", "p", "s"])
    if user not in possible_choices:
        print('Uh oh! Please select a valid option', play())

entire code:

import random

game_loop = True


def play():
    user = input(
        "What's your choice? 'r' for rock, 'p' for paper, 's' for scissors: "
    ).lower
    computer = random.choice(["r", "p", "s"])

    if user == computer:
        return f"Tie! Computer chose {computer}"

    # r > s, s > p, p > r
    if win_or_lose(user, computer):
        return f"You won! Computer chose {computer}"
    return f"You lost! Computer chose {computer}"


def win_or_lose(player, opponent):

    if (
        (player == "r" and opponent == "s")
        or (player == "s" and opponent == "p")
        or (player == "p" and opponent == "r")
    ):
        return True


def play_again():
    p_a = input("Play again? (y/n): ")
    if p_a == "y":
        print(play())
    elif p_a == "n":
        quit()
    else:
        print("oof! Please choose correct option: (y/n)")
        play_again()


print(play())

while game_loop == True:
    play_again()

Answer 1

I recommend a while loop, implemented like this:

def play():
    choices = ['r','p','s']
    while True:
        user = input(
            "What's your choice? 'r' for rock, 'p' for paper, 's' for scissors: "
        ).lower()
        if user in choices:
            break
        else:
            print('choose again')
            continue
...

This structure checks if the input is in the list of choices, and if it is not the user tries again. Also the parenthesis on the.lower() were added.

Some more information on this type of thing can be found here

Answer 2

Answer:

def play():
    choices = ["r", "p", "s"]
    computer = random.choice(["r", "p", "s"])
    while True:
        user = input(
            "What's your choice? 'r' for rock, 'p' for paper, 's' for scissors: "
        )
        if user in choices:
            break
        else:
            print("Please choose a correct choice.")
            continue

    if user == computer:
        return f"Tie! Computer chose {computer}"

    # r > s, s > p, p > r
    if win_or_lose(user, computer):
        return f"You won! Computer chose {computer}"
    return f"You lost! Computer chose {computer}"


def win_or_lose(player, opponent):

    if (
        (player == "r" and opponent == "s")
        or (player == "s" and opponent == "p")
        or (player == "p" and opponent == "r")
    ):
        return True


def play_again():
    while True:
        p_a = input("Play again? (y/n): ")
        if p_a == "y":
            print(play())
        elif p_a == "n":
            quit()
        else:
            print("Please choose correct option..")
        play_again()


print(play())

while True:
    play_again()