def get_first_digit_index(string: str):
    """
    Find index of first non digit char from right to left

    :param string: input string
    :return: index of first non digit char or None
    """
    for i in range(-1, -1 * len(string) - 1, -1):
        if not string[i].isdigit():
            return i + 1
    return None