def __calculate_flight_time(departure_time=None, arrival_time=None):
    """
    This function calculates total flight time for a single leg

    :return: (str) Flight time in hour and minutes
    """
    dtime = departure_time
    atime = arrival_time
    flight_time_sec = atime - dtime
    minutes, seconds = divmod(flight_time_sec, 60)
    hours, minutes = divmod(minutes, 60)
    total_flight_time = str(hours) + 'h' + ' ' + str(minutes) + 'm'
    return total_flight_time
