爬取伯樂在線文章（二）經過xpath提取源文件中須要的內容

爬取說明

以單個頁面爲例，如：http://blog.jobbole.com/110287/

咱們能夠提取標題、日期、多少個評論、正文內容等

Xpath介紹

1.　xpath簡介

（1）　xpath使用路徑表達式在xml和html中進行導航

（2）　xpath包含標準函數庫

（3）　xpath是一個w3c標準

2.　Xpath的節點關係

（1）　父節點

（2）　子節點

（3）　同胞節點

（4）　先輩節點

（5）　後代節點

3.　Xpath語法

開始爬取

1.　將starts_urls修改成http://blog.jobbole.com/110287/

2.　def parse(self, response)方法中的response自帶有xpath方法

結果爲：//*[@id="post-110287"]/div[1]/h1

 在parse方法裏面進行解析：

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

斷點查看返回的title_selector的類型是SelectorList，裏面存放的是一個selector，爲何不直接返回一個node類型，這是由於咱們獲取的h1下面可能還有不少層，咱們能夠進一步的作xpath篩選，直接返回node的話就沒法作xpath篩選，因此scrapy作了進一步的封裝，能夠讓咱們進一步進行xpath篩選。

咱們能夠看到data裏面的值是一個h1標籤，咱們能夠直接調用一個text()函數獲取裏面的值，以下

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

 此時在看data裏面值就是咱們須要的內容了

調試Xpath

在scarpy裏面進行調試是比較慢的，scrapy提供了一種shell模式，能夠在裏面對某個URL進行調試，以下在cmd裏面

(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
>>>

View Code

使用以下

獲取data裏面值能夠用Selector的extract方法，返回的是一個數組

在獲取數組裏面的第一個值就能夠獲取咱們須要的內容