Returns string such as 1h 05m 55s.

def seconds2str(seconds):
    """Returns string such as 1h 05m 55s."""

    if seconds < 0:
        return "{0:.3g}s".format(seconds)
    elif math.isnan(seconds):
        return "NaN"
    elif math.isinf(seconds):
        return "Inf"

    m, s = divmod(seconds, 60)
    h, m = divmod(m, 60)
    if h >= 1:
        return "{0:g}h {1:02g}m {2:.3g}s".format(h, m, s)
    elif m >= 1:
        return "{0:02g}m {1:.3g}s".format(m, s)
    else:
        return "{0:.3g}s".format(s)