Args:
        isbn (str/list): ISBN number as string or list of digits.

    Warning:
        Function expects that `isbn` is only 12 digits long.

    Returns:
        int: Last checksum digit for given `isbn`.

def get_isbn13_checksum(isbn):
    """
    Args:
        isbn (str/list): ISBN number as string or list of digits.

    Warning:
        Function expects that `isbn` is only 12 digits long.

    Returns:
        int: Last checksum digit for given `isbn`.
    """
    multipliers = map(lambda x: int(x), list("13" * 6))

    rest = sum([i * x for i, x in zip(multipliers, isbn)]) % 10

    if rest == 0:
        return rest

    return 10 - rest