def get_30_360(start, end):
    """ implements 30/360 Day Count Convention. """
    start_day = min(start.day, 30)
    end_day = 30 if (start_day == 30 and end.day == 31) else end.day
    return (360 * (end.year - start.year) + 30 * (end.month - start.month) + (end_day - start_day)) / 360.0