爬取伯乐在线文章（二）通过xpath提取源文件中需要的内容

爬取说明

以单个页面为例，如：http://blog.jobbole.com/110287/

我们可以提取标题、日期、多少个评论、正文内容等

Xpath介绍

1.　xpath简介

（1）　xpath使用路径表达式在xml和html中进行导航

（2）　xpath包含标准函数库

（3）　xpath是一个w3c标准

2.　Xpath的节点关系

（1）　父节点

（2）　子节点

（3）　同胞节点

（4）　先辈节点

（5）　后代节点

3.　Xpath语法

开始爬取

1.　将starts_urls修改为http://blog.jobbole.com/110287/

2.　def parse(self, response)方法中的response自带有xpath方法

结果为：//*[@id="post-110287"]/div[1]/h1

在parse方法里面进行解析：

 #业务逻辑
    def parse(self, response):
        title_selector = response.xpath('//*[@id="post-110287"]/div[1]/h1')
        pass

断点查看返回的title_selector的类型是SelectorList，里面存放的是一个selector，为什么不直接返回一个node类型，这是因为我们获取的h1下面可能还有很多层，我们可以进一步的做xpath筛选，直接返回node的话就无法做xpath筛选，所以scrapy做了进一步的封装，可以让我们进一步进行xpath筛选。

我们可以看到data里面的值是一个h1标签，我们可以直接调用一个text()函数获取里面的值，如下

title_selector = response.xpath('//*[@id="post-110287"]/div[1]/h1/text()')

此时在看data里面值就是我们需要的内容了

调试Xpath

在scarpy里面进行调试是比较慢的，scrapy提供了一种shell模式，可以在里面对某个URL进行调试，如下在cmd里面

(scrapyenv) E:\Python\Envs\EnterpriseSpider>scrapy shell http://blog.jobbole.com/110287/

(scrapyenv) E:\Python\Envs\EnterpriseSpider>scrapy shell http://blog.jobbole.com/110287/
2018-11-05 10:14:15 [scrapy.utils.log] INFO: Scrapy 1.5.1 started (bot: EnterpriseSpider)
2018-11-05 10:14:15 [scrapy.utils.log] INFO: Versions: lxml 4.2.5.0, libxml2 2.9.5, cssselect 1.0.3, parsel 1.5.1, w3lib 1.19.0, Twisted 18.9.0, Python 3.6.6 (v3.6.6:4cf1f54eb7, Jun 27 2018, 03:37:03) [MSC v.1900 64 bit (AMD64)], pyOpenSSL 18.0.0 (OpenSSL 1.1.0i  14 Aug 2018), cryptography 2.3.1, Platform Windows-10-10.0.17134-SP0
2018-11-05 10:14:15 [scrapy.crawler] INFO: Overridden settings: {'BOT_NAME': 'EnterpriseSpider', 'DUPEFILTER_CLASS': 'scrapy.dupefilters.BaseDupeFilter', 'LOGSTATS_INTERVAL': 0, 'NEWSPIDER_MODULE': 'EnterpriseSpider.spiders', 'SPIDER_MODULES': ['EnterpriseSpider.spiders']}
2018-11-05 10:14:15 [scrapy.middleware] INFO: Enabled extensions:
['scrapy.extensions.corestats.CoreStats',
 'scrapy.extensions.telnet.TelnetConsole']
2018-11-05 10:14:15 [scrapy.middleware] INFO: Enabled downloader middlewares:
['scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware',
 'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware',
 'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware',
 'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware',
 'scrapy.downloadermiddlewares.retry.RetryMiddleware',
 'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware',
 'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware',
 'scrapy.downloadermiddlewares.redirect.RedirectMiddleware',
 'scrapy.downloadermiddlewares.cookies.CookiesMiddleware',
 'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware',
 'scrapy.downloadermiddlewares.stats.DownloaderStats']
2018-11-05 10:14:15 [scrapy.middleware] INFO: Enabled spider middlewares:
['scrapy.spidermiddlewares.httperror.HttpErrorMiddleware',
 'scrapy.spidermiddlewares.offsite.OffsiteMiddleware',
 'scrapy.spidermiddlewares.referer.RefererMiddleware',
 'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware',
 'scrapy.spidermiddlewares.depth.DepthMiddleware']
2018-11-05 10:14:15 [scrapy.middleware] INFO: Enabled item pipelines:
[]
2018-11-05 10:14:15 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
2018-11-05 10:14:15 [scrapy.core.engine] INFO: Spider opened
2018-11-05 10:14:15 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.jobbole.com/110287/> (referer: None)
[s] Available Scrapy objects:
[s]   scrapy     scrapy module (contains scrapy.Request, scrapy.Selector, etc)
[s]   crawler    <scrapy.crawler.Crawler object at 0x000002C00C180080>
[s]   item       {}
[s]   request    <GET http://blog.jobbole.com/110287/>
[s]   response   <200 http://blog.jobbole.com/110287/>
[s]   settings   <scrapy.settings.Settings object at 0x000002C00E7DD898>
[s]   spider     <JobboleSpider 'jobbole' at 0x2c00ea8b160>
[s] Useful shortcuts:
[s]   fetch(url[, redirect=True]) Fetch URL and update local objects (by default, redirects are followed)
[s]   fetch(req)                  Fetch a scrapy.Request and update local objects
[s]   shelp()           Shell help (print this help)
[s]   view(response)    View response in a browser
>>>