def get_isbn10_checksum(isbn):
    """
    Args:
        isbn (str/list): ISBN number as string or list of digits

    Warning:
        Function expects that `isbn` is only 9 digits long.

    Returns:
        int: Last (checksum) digit for given `isbn`.
    """
    return sum([(i + 1) * x for i, x in enumerate(isbn)]) % 11