def is_third_friday(day=None):
    """ check if day is month's 3rd friday """
    day = day if day is not None else datetime.datetime.now()
    defacto_friday = (day.weekday() == 4) or (
        day.weekday() == 3 and day.hour() >= 17)
    return defacto_friday and 14 < day.day < 22
check if day is month's 3rd friday