vault

def vault() -> bool:

    pin = "".join([random.choice("0123456789abcdef") for _ in range(4)])
    digits = ["z", "z", "z", "z"]
    counter = 0

    print("What is the 4-digit PIN?")

    while True:

        attempt = list(input("Attempt> "))

        for _ in range(len(attempt)):

            digits.insert(0, attempt.pop())
            digits.pop()

            if "".join(digits) == pin:
                return True

            counter += 1
            if counter > MAX_DIGITS:
                return False

    return False