抓取链接页面中的额外字段

Question

我正在尝试在主页上抓取一些帖子，其中几乎所有我需要的东西都在那里。但是在链接（ed）页面上，我还需要一个日期字段。我尝试了以下回调：

from scrapy.spider import BaseSpider
from macnn_com.items import MacnnComItem

from scrapy.selector import HtmlXPathSelector
from scrapy.contrib.loader import XPathItemLoader
from scrapy.contrib.loader.processor import MapCompose, Join
from scrapy.http.request import Request

class MacnnSpider(BaseSpider):
    name = 'macnn_com'
    allowed_domains = ['macnn.com']
    start_urls = ['http://www.macnn.com']
    posts_list_xpath = '//div[@class="post"]'
    item_fields = { 'title': './/h1/a/text()',
                    'link': './/h1/a/@href',
                    'summary': './/p/text()',
                    'image': './/div[@class="post_img"]/div[@class="post_img_border"]/a/img/@original' }

    def parse(self, response):
        hxs = HtmlXPathSelector(response)
        # iterate over posts
        for qxs in hxs.select(self.posts_list_xpath):
            loader = XPathItemLoader(MacnnComItem(), selector=qxs)

            # define processors
            loader.default_input_processor = MapCompose(unicode.strip)
            loader.default_output_processor = Join()
            # skip posts with empty titles
            if loader.get_xpath('.//h1/a/text()') == []:
                continue
            # iterate over fields and add xpaths to the loader
            for field, xpath in self.item_fields.iteritems():
                loader.add_xpath(field, xpath)
            request = Request(loader.get_xpath('.//h1/a/@href')[0], callback=self.parse_link,meta={'loader':loader})
            yield request
            #loader.add_value('datums',request)
            yield loader.load_item()

    def parse_link(self, response):
        loader = response.meta["loader"]
        hxs = HtmlXPathSelector(response)
        hero = hxs.select("//div[@class='post_header']/h2/text()").extract()
        loader.add_value('datums',hero)
        return loader

但我收到类似的错误

错误：Spider 必须返回 Request、BaseItem 或 None，在 <GET http://www.macnn.com/articles/13/06/14/sidebar.makes.it.easier.to.jump.between.columns/> 中获得了“XPathItemLoader”

我在这里做错了什么？

Answer 1

parse_link 需要返回一个项目，而不是加载程序。

def parse_link(self, response):
    loader = response.meta["loader"]
    hxs = HtmlXPathSelector(response)
    hero = hxs.select("//div[@class='post-header']/h2/text()").extract()
    loader.add_value('datums',hero)
    return loader.load_item()