使用 Scrapy 抓取网站时使用 Xpath 的困惑

Question

在尝试抓取网站的某些元素时，我无法理解要选择 Xpath 的哪个部分。在这种情况下，我正在尝试抓取本文中链接的所有网站（例如，xpath 的这一部分：

data-track="Body Text Link: External" href="http://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/brca-related-cancer-risk-assessment-genetic-counseling-and-genetic-testing">

我的蜘蛛可以工作，但它不会刮任何东西！

我的代码如下：

import scrapy
from scrapy.selector import Selector

from nymag.items import nymagItem

class nymagSpider(scrapy.Spider):
    name = 'nymag'
    allowed_domains = ['http://wwww.nymag.com']
    start_urls = ["http://nymag.com/thecut/2015/09/should-we-all-get-the-breast-cancer-gene-test.html"]

    def parse(self, response):
        #I'm pretty sure the below line is the issue
        links = Selector(response).xpath(//*[@id="primary"]/main/article/div/span)
        for link in links:
            item = nymagItem()
            #This might also be wrong - am trying to extract the href section
            item['link'] = question.xpath('a/@href').extract()
            yield item

Answer 1

有一个更简单的方法。获取所有具有data-track 和href 属性的a 元素：

In [1]: for link in response.xpath("//div[@id = 'primary']/main/article//a[@data-track and @href]"):
    print link.xpath("@href").extract()[0]
   ...:     
//nymag.com/tags/healthcare/
//nymag.com/author/Susan%20Rinkunas/
http://twitter.com/sueonthetown
http://www.facebook.com/sharer/sharer.php?u=http://nymag.com/thecut/2015/09/should-we-all-get-the-breast-cancer-gene-test.html%3Fmid%3Dfb-share-thecut
https://twitter.com/share?text=Should%20All%20Women%20Get%20Tested%20for%20the%20Breast%20Cancer%20Gene%3F&url=http://nymag.com/thecut/2015/09/should-we-all-get-the-breast-cancer-gene-test.html%3Fmid%3Dtwitter-share-thecut&via=TheCut
https://plus.google.com/share?url=http%3A%2F%2Fnymag.com%2Fthecut%2F2015%2F09%2Fshould-we-all-get-the-breast-cancer-gene-test.html
http://pinterest.com/pin/create/button/?url=http://nymag.com/thecut/2015/09/should-we-all-get-the-breast-cancer-gene-test.html%3Fmid%3Dpinterest-share-thecut&description=Should%20All%20Women%20Get%20Tested%20for%20the%20Breast%20Cancer%20Gene%3F&media=http:%2F%2Fpixel.nymag.com%2Fimgs%2Ffashion%2Fdaily%2F2015%2F09%2F08%2F08-angelina-jolie.w750.h750.2x.jpg
whatsapp://send?text=Should%20All%20Women%20Get%20Tested%20for%20the%20Breast%20Cancer%20Gene%3F%0A%0Ahttp%3A%2F%2Fnymag.com%2Fthecut%2F2015%2F09%2Fshould-we-all-get-the-breast-cancer-gene-test.html&mid=whatsapp
mailto:?subject=Should%20All%20Women%20Get%20Tested%20for%20the%20Breast%20Cancer%20Gene%3F&body=I%20saw%20this%20on%20The%20Cut%20and%20thought%20you%20might%20be%20interested...%0A%0AShould%20All%20Women%20Get%20Tested%20for%20the%20Breast%20Cancer%20Gene%3F%0AIt's%20not%20a%20crystal%20ball.%0Ahttp%3A%2F%2Fnymag.com%2Fthecut%2F2015%2F09%2Fshould-we-all-get-the-breast-cancer-gene-test.html%3Fmid%3Demailshare%5Fthecut
...