def hhmmss(sec_in):
    """
    Convert elapsed time in seconds to "d days hh:mm:ss.ss" format.
    This is nice for things that take a long time.
    """
    h = int(sec_in // 3600)
    m = int(sec_in % 3600 // 60)
    s = sec_in % 3600 % 60
    if h < 24:
        hstr = "{0:0>2}".format(h)
    elif h >= 24 and h < 48:
        hstr = "1 day {0:0>2}".format(h % 24)
    else:
        hstr = "{0} days {1:0>2}".format(h // 24, h % 24)
    return "{0}:{1:0>2}:{2:0>5.2f}".format(hstr, m, s)