code: def best_four_point(self):
          
          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
docs: 判斷買點或賣點
  
              :rtype: tuple
              :returns: (bool, str)