Scrapy爬虫框架第四讲(Linux环境）【Selector的使用】

下面我们来学习Selector的具体使用：（参考文档：http://scrapy-chs.readthedocs.io/zh_CN/1.0/topics/selectors.html）

Selector简介：Scrapy框架提供了自己的一套数据提取方法即Selector（选择器），它是基于lxml构建的，支持xpath、css、正则表达式

下面我们主要介绍Selector与scrapy shell(scrapy中的交互模式)并结合xpath 、css 、正则表达式的使用

（1）、启动终端并激活虚拟环境

（2）、使用scrapy shell 下载网站例子这里我已百度阅读畅销榜为例进行分析（scrapy shell https://yuedu.baidu.com/rank/hotsale?pn=0---爬取该网站，再使用fetch（‘https://yuedu.baidu.com/ebook/09075cc5a1116c175f0e7cd184254b35effd1a77?fr=bookrank’）下载具体一本书的页面）

(course-python3.5-env) bourne@bourne-vm:~/example/example$ scrapy shell https://yuedu.baidu.com/rank/hotsale?pn=0
2018-05-14 10:56:08 [scrapy.utils.log] INFO: Scrapy 1.5.0 started (bot: example)
2018-05-14 10:56:08 [scrapy.utils.log] INFO: Versions: lxml 4.2.1.0, libxml2 2.9.8, cssselect 1.0.3, parsel 1.4.0, w3lib 1.19.0, Twisted 18.4.0, Python 3.5.2 (default, Nov 23 2017, 16:37:01) - [GCC 5.4.0 20160609], pyOpenSSL 17.5.0 (OpenSSL 1.1.0h  27 Mar 2018), cryptography 2.2.2, Platform Linux-4.13.0-36-generic-x86_64-with-Ubuntu-16.04-xenial
2018-05-14 10:56:08 [scrapy.crawler] INFO: Overridden settings: {'BOT_NAME': 'example', 'LOGSTATS_INTERVAL': 0, 'DUPEFILTER_CLASS': 'scrapy.dupefilters.BaseDupeFilter', 'USER_AGENT': 'BaiduSpider', 'ROBOTSTXT_OBEY': True, 'SPIDER_MODULES': ['example.spiders'], 'NEWSPIDER_MODULE': 'example.spiders'}
2018-05-14 10:56:08 [scrapy.middleware] INFO: Enabled extensions:
['scrapy.extensions.memusage.MemoryUsage',
 'scrapy.extensions.corestats.CoreStats',
 'scrapy.extensions.telnet.TelnetConsole']
2018-05-14 10:56:08 [scrapy.middleware] INFO: Enabled downloader middlewares:
['scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware',
 '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']
2018-05-14 10:56:08 [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']
2018-05-14 10:56:08 [scrapy.middleware] INFO: Enabled item pipelines:
[]
2018-05-14 10:56:08 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
2018-05-14 10:56:08 [scrapy.core.engine] INFO: Spider opened
2018-05-14 10:56:08 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://yuedu.baidu.com/robots.txt> (referer: None)
2018-05-14 10:56:09 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://yuedu.baidu.com/rank/hotsale?pn=0> (referer: None)
[s] Available Scrapy objects:
[s]   scrapy     scrapy module (contains scrapy.Request, scrapy.Selector, etc)
[s]   crawler    <scrapy.crawler.Crawler object at 0x7f603750edd8>
[s]   item       {}
[s]   request    <GET https://yuedu.baidu.com/rank/hotsale?pn=0>
[s]   response   <200 https://yuedu.baidu.com/rank/hotsale?pn=0>
[s]   settings   <scrapy.settings.Settings object at 0x7f603750eb38>
[s]   spider     <DefaultSpider 'default' at 0x7f60370a54a8>
[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
In [1]: fetch('https://yuedu.baidu.com/ebook/09075cc5a1116c175f0e7cd184254b35effd1a77?fr=b
   ...: ookrank')
2018-05-14 10:56:34 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://yuedu.baidu.com/ebook/09075cc5a1116c175f0e7cd184254b35effd1a77?fr=bookrank> (referer: None)