def format_id(kepler_id):
    """Formats the id to be a zero padded integer with a length of 9 characters.
    No ID is greater than 9 digits and this function will throw a ValueError
    if such an integer is given.
    :kepler_id: The Kepler ID as an integer.
    :returns: A 0 padded formatted string of length 9.
    """
    return f'{kepler_id:09d}'