def fmt_second(time_total):
    """
    >>> fmt_second(100)
    '00:01:40'
    """

    def _ck(t):
        return t < 10 and "0%s" % t or t

    times = int(time_total)
    h = times / 3600
    m = times % 3600 / 60
    s = times % 3600 % 60
    return "%s:%s:%s" % (_ck(h), _ck(m), _ck(s))