timedelta = [("d", 24*3600), ("h", 3600), ("m", 60), ("s", 1)]
def duration_to_string(duration: float) -> str:
    """
    Convert a duration in seconds to a string of the form "<days>d <hours>h <minutes>m <seconds>s"
    where only the largest units are included.
    Parameters
    ----------
    duration: float
        Duration in seconds.

    Returns
    -------
       String representation of the duration.
    """
    include = False
    s = ""
    sign = 1 if duration > 0 else -1
    time_left = abs(int(duration))
    for i, (unit, unit_seconds) in enumerate(timedelta):
        t = int(time_left / unit_seconds)
        if t != 0 or include or unit == "s":
            s += f"{sign*t:02}{unit} "
            include = True
        time_left %= unit_seconds
    return s.strip()