Exploring Kaprekar's constant

kaprekar.py

import random
from typing import Optional


def main() -> None:
    run_number: int = 0
    run_amount: int = 10_000
    count_total: int = 0

    while run_number < run_amount:
        count: Optional[int] = kaprekar()

        if count:
            count_total += count
            run_number += 1

    average: float = count_total / run_amount

    print(average)
    print(average <= 7)


def kaprekar() -> Optional[int]:
    count: int = 0
    number: int = random.randint(1000, 9999)
    KAPREKARS_CONSTANT: int = 6174

    while number != KAPREKARS_CONSTANT:
        digit_strings: list[str] = [digit for digit in str(number)]

        if len(set(digit_strings)) == 1:
            # In this case, the random number digits were all the same (Ex: 9999)
            # This will result in an infinite loop, so we should return and not count this run
            return None

        digit_strings_ascending: list[str] = sorted(digit_strings, key=int)
        digit_strings_descending: list[str] = list(reversed(digit_strings_ascending))

        smallest_number: int = int("".join(digit_strings_ascending))
        largest_number: int = int("".join(digit_strings_descending))

        number = largest_number - smallest_number
        count += 1

    assert(count <= 7)

    return count


if __name__ == "__main__":
    main()