def best_four_point(self):
        """ 判斷買點或賣點

            :rtype: tuple
            :returns: (bool, str)
        """
        buy = self.best_four_point_to_buy()
        sell = self.best_four_point_to_sell()

        if buy:
            return True, buy
        elif sell:
            return False, sell

        return None