def repr_timespan(start, end) ->str:
    """return a string representing the timespan.

    Returns:
        a string like #h#m

    """
    duration = end - start
    hours = duration.seconds // 3600
    minutes = (duration.seconds - hours * 3600) // 60
    hours += duration.days * 24
    return '{}:{:02}'.format(hours, minutes)
