使用以下代码，可以准确地获取所有值本身。但是，检索值的一部分（折换日期）无法由ItemLoader处理，因此按原样输出。
经过各种验证后，我们发现在parse_firstpage_item中获得的值似乎没有传递到Itemloader。由parse_productpage_item检索到的每个项都得到了正确的处理。
我已经验证了Itemloader中的处理器描述也是正确的，因为如果将值传递给Itemloader，输出将以所需的形式输出。
因此，我假设对蜘蛛的描述有问题。
我是一个初学者，所以真的很难理解数据是如何在Scrapy上处理的...

class AllSaledataSpider(CrawlSpider):
    name = 'all_salesdata_copy'
    allowed_domains = ['www.buyma.com']

    #Read from shopper URL list saved in csv file
def start_requests(self):
         with open('/Users/morni/BUYMA/buyma_researchtool/AllshoppersURL.csv', 'r', encoding='utf-8-sig') as f:
            reader = csv.reader(f)
            for row in reader:
                for n in range(1, 3): #300
                    url =str((row[2])[:-5]+'/sales_'+str(n)+'.html')
                    # f'{self.base_page}{row}/sales_{n}.html'
                    yield scrapy.Request(
                        url=url,
                        callback=self.parse_firstpage_item,
                        # errback=self.errback_httpbin,
                        dont_filter=True
                        )

# Obtain the 30 product links on the order history page, and the date of sign-up (obtained here, since they are not listed on the individual product pages), store these two pieces of information in item, and pass the request to the next parsing method.

    def parse_firstpage_item(self, response): 
            conversion_date = response.xpath('//*[@id="buyeritemtable"]/div/ul/li[2]/p[3]/text()').getall()
            product_url = response.xpath('//*[@id="buyeritemtable"]/div/ul/li[2]/p[1]/a/@href').getall()
            for i in range(2):
                loader = ItemLoader(item = BuymaResearchtoolItem(), response = response)
                loader.add_value("conversion_date", conversion_date[i])
                loader.add_value("product_url", product_url[i])
                item = loader.load_item()
                yield scrapy.Request(
                    url=response.urljoin(item["product_url"][-1]),
                    callback=self.parse_productpage_item,
                    cb_kwargs={'item': item},
                    )

 #Retrieve the content in the product detail page and merge it with the previously retrieved information

       def parse_productpage_item(self, response, item): 
                loader = ItemLoader(item=item, response = response)
                loader.add_xpath("product_name", 'normalize-space(//li[@class="page_ttl"]/span[1]/text())')
                loader.add_xpath("brand_name", 'normalize-space(//[@id="s_brand"]/dd/a/text())')
    〜〜

                    yield loader.load_item()

Itemloader的过程如下

def strip_n(element):
    if element:
        return element.replace('\t', '').replace('\n', '')
    return element

def conversion_dates(element):
        if element:
            str = element.replace('成約日：', '')
            dte = datetime.datetime.strptime(str, '%Y/%m/%d')
            return dte
        return element

class BuymaResearchtoolItem(scrapy.Item):

# first_page

    conversion_date = scrapy.Field(
        input_processors = MapCompose(conversion_dates),
        output_processors = TakeFirst()
    )
    product_url = scrapy.Field(
        output_processors = TakeFirst()
        )

# product_page

product_name = scrapy.Field(
        input_processors = MapCompose(strip_n),
        output_processors = TakeFirst()
    )
brand_name = scrapy.Field(
        input_processors = MapCompose(strip_n),
        output_processors = TakeFirst()
    )