Python爬虫系列之----Scrapy(五)网页提取的三种方式(正则,Beautiful Soup,Lxml)

来源：互联网发布：吕梁离石区大数据招聘编辑：程序博客网时间：2024/05/05 10:51

一、提取方式

从网页中提取数据有很多方法,概况起来大概有这么三种方式,首先是正则,然后是流行的Beautiful Soup模块,最后是强大的Lxml模块。

1、正则表达式:最原始的方法,通过编写一些正则表达式,然后从HTML/XML中提取数据。

2、Beautiful Soup模块:Beautiful Soup 是一个可以从 HTML 或 XML 文件中提取数据的 Python 库.它能够通过你喜欢的转换器实现惯用的文档导航,查找,修改文档的方式.Beautiful Soup 会帮你节省数小时甚至数天的工作时间。

3、Lxml模块:lxml是基于libxm12这一XML解析库的Python封装,该模块使用C语言编写,解析速读比Beautiful Soup模块快，不过安装更为复杂。

Scrapy使用了一种基于 XPath 和 CSS 表达式机制: Scrapy Selectors。关于selector和其他提取机制的信息请参考 Selector文档

这里给出XPath表达式的例子及对应的含义:

/html/head/title: 选择HTML文档中 <head> 标签内的 <title> 元素
/html/head/title/text(): 选择上面提到的 <title> 元素的文字
//td: 选择所有的 <td> 元素
//div[@class="mine"]: 选择所有具有 class="mine" 属性的 div 元素

上边仅仅是几个简单的XPath例子，XPath实际上要比这远远强大的多。如果您想了解的更多，我们推荐这篇XPath教程。

为了配合XPath，Scrapy除了提供了 Selector 之外，还提供了方法来避免每次从response中提取数据时生成selector的麻烦。

Selector有四个基本的方法(点击相应的方法可以看到详细的API文档):

xpath(): 传入xpath表达式，返回该表达式所对应的所有节点的selector list列表。
css(): 传入CSS表达式，返回该表达式所对应的所有节点的selector list列表.
extract(): 序列化该节点为unicode字符串并返回list。
re(): 根据传入的正则表达式对数据进行提取，返回unicode字符串list列表。

在Shell中尝试Selector选择器

为了介绍Selector的使用方法，接下来我们将要使用内置的 Scrapy shell 。Scrapy Shell需要您预装好IPython(一个扩展的Python终端,可通过命令安装: pip install ipython)。

您需要进入项目的根目录，执行下列命令来启动shell:

scrapy shell "http://blog.csdn.net/u011781521/article/details/70182815"

注意:当您在终端运行Scrapy时，请一定记得给url地址加上引号，否则包含参数的url(例如 & 字符)会导致Scrapy运行失败。

shell的输出:

G:\Scrapy_work\myfendo>scrapy shell "http://blog.csdn.net/u011781521/article/details/70182815"2017-04-15 21:01:18 [scrapy.utils.log] INFO: Scrapy 1.3.3 started (bot: myfendo)2017-04-15 21:01:18 [scrapy.utils.log] INFO: Overridden settings: {'BOT_NAME': 'myfendo', 'DUPEFILTER_CLASS': 'scrapy.dupefilters.BaseDupeFilter', 'LOGSTATS_INTERVAL': 0, 'NEWSPIDER_MODULE': 'myfendo.spiders', 'ROBOTSTXT_OBEY': True, 'SPIDER_MODULES': ['myfendo.spiders']}2017-04-15 21:01:18 [scrapy.middleware] INFO: Enabled extensions:['scrapy.extensions.corestats.CoreStats', 'scrapy.extensions.telnet.TelnetConsole']2017-04-15 21:01:19 [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.stats.DownloaderStats']2017-04-15 21:01:19 [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']2017-04-15 21:01:19 [scrapy.middleware] INFO: Enabled item pipelines:[]2017-04-15 21:01:19 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:60232017-04-15 21:01:19 [scrapy.core.engine] INFO: Spider opened2017-04-15 21:01:19 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/robots.txt> (referer: None)2017-04-15 21:01:19 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/u011781521/article/details/70182815> (referer: None)2017-04-15 21:01:20 [traitlets] DEBUG: Using default logger2017-04-15 21:01:20 [traitlets] DEBUG: Using default logger[s] Available Scrapy objects:[s]   scrapy     scrapy module (contains scrapy.Request, scrapy.Selector, etc)[s]   crawler    <scrapy.crawler.Crawler object at 0x000002B5B7E512E8>[s]   item       {}[s]   request    <GET http://blog.csdn.net/u011781521/article/details/70182815>[s]   response   <200 http://blog.csdn.net/u011781521/article/details/70182815>[s]   settings   <scrapy.settings.Settings object at 0x000002B5B8E1DB38>[s]   spider     <DefaultSpider 'default' at 0x2b5b909f358>[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 browserIn [1]:

当shell载入后，您将得到一个包含response数据的本地 response 变量。输入 response.body 将输出response的包体

输入 response.headers 可以看到response的包头。

更为重要的是，当输入 response.selector 时，您将获取到一个可以用于查询返回数据的selector(选择器)，以及映射到 response.selector.xpath() 、 response.selector.css() 的快捷方法(shortcut): response.xpath() 和 response.css() 。

同时，shell根据response提前初始化了变量 sel 。该selector根据response的类型自动选择最合适的分析规则(XML vs HTML)。

让我们来试试:

In [4]: response.xpath('//title')Out[4]: [<Selector xpath='//title' data='<title>Python爬虫系列之----Scrapy(一)爬虫原理 - fe'>]In [5]: response.xpath('//title').extract()Out[5]: ['<title>Python爬虫系列之----Scrapy(一)爬虫原理 - fendo\r\n        - 博客频道 - CSDN.NET</title>']In [6]: response.xpath('//title/text()')Out[6]: [<Selector xpath='//title/text()' data='Python爬虫系列之----Scrapy(一)爬虫原理 - fendo\r\n  '>]In [7]: response.xpath('//title/text()').extract()Out[7]: ['Python爬虫系列之----Scrapy(一)爬虫原理 - fendo\r\n        - 博客频道 - CSDN.NET']

二、提取数据

让我们从返回的response中提取数据，可以结合Firebug来观察HTML源码并确定合适的XPath表达式

文章的标题:

response.xpath('//h1/span/a/text()').extract()

输出的结果为:

网页中的链接:

response.xpath("//span/a[@href='https://scrapy.org/']/text()").extract()

输出结果为:

网页的描述:

response.xpath("//meta[@name='description']").extract()

输出结果为:

三、使用Item

Item 对象是自定义的python字典。您可以使用标准的字典语法来获取到其每个字段的值。(字段即是我们之前用Field赋值的属性):

一般来说，Spider将会将爬取到的数据以 Item 对象返回。所以为了将爬取的数据返回，我们最终的代码将是:

# -*- coding: utf-8 -*-import scrapyfrom myfendo.items import MyfendoItemclass MyfendosSpider(scrapy.Spider):    name = "myfendos"    allowed_domains = ["csdn.net"]    start_urls = [        "http://blog.csdn.net/u011781521/article/details/70182815",    ]    def parse(self, response):        item=MyfendoItem()        item['title']=response.xpath('//h1/span/a/text()')        item['link']=response.xpath("//span/a[@href='https://scrapy.org/']/text()")        item['desc']=response.xpath("//meta[@name='description']")        yield item

现在运行爬虫将会产生 MyfendoItem对象:

G:\Scrapy_work\myfendo>scrapy crawl myfendos2017-04-15 21:50:54 [scrapy.utils.log] INFO: Scrapy 1.3.3 started (bot: myfendo)2017-04-15 21:50:54 [scrapy.utils.log] INFO: Overridden settings: {'BOT_NAME': 'myfendo', 'NEWSPIDER_MODULE': 'myfendo.spiders', 'ROBOTSTXT_OBEY': True, 'SPIDER_MODULES': ['myfendo.spiders']}2017-04-15 21:50:54 [scrapy.middleware] INFO: Enabled extensions:['scrapy.extensions.corestats.CoreStats', 'scrapy.extensions.telnet.TelnetConsole', 'scrapy.extensions.logstats.LogStats']2017-04-15 21:50:54 [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.stats.DownloaderStats']2017-04-15 21:50:54 [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']2017-04-15 21:50:54 [scrapy.middleware] INFO: Enabled item pipelines:[]2017-04-15 21:50:54 [scrapy.core.engine] INFO: Spider opened2017-04-15 21:50:54 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)2017-04-15 21:50:54 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:60242017-04-15 21:50:55 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/robots.txt> (referer: None)2017-04-15 21:50:55 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/u011781521/article/details/70182815> (referer: None)2017-04-15 21:50:55 [scrapy.core.scraper] DEBUG: Scraped from <200 http://blog.csdn.net/u011781521/article/details/70182815>{'desc': [<Selector xpath="//meta[@name='description']" data='<meta name="description" content="一、Scra'>], 'link': [<Selector xpath="//span/a[@href='https://scrapy.org/']/text()" data='https://scrapy.org/'>], 'title': [<Selector xpath='//h1/span/a/text()' data='\r\n        Python爬虫系列之----Scrapy(一)爬虫原理  '>]}2017-04-15 21:50:55 [scrapy.core.engine] INFO: Closing spider (finished)2017-04-15 21:50:55 [scrapy.statscollectors] INFO: Dumping Scrapy stats:{'downloader/request_bytes': 467, 'downloader/request_count': 2, 'downloader/request_method_count/GET': 2, 'downloader/response_bytes': 17315, 'downloader/response_count': 2, 'downloader/response_status_count/200': 2, 'finish_reason': 'finished', 'finish_time': datetime.datetime(2017, 4, 15, 13, 50, 55, 392037), 'item_scraped_count': 1, 'log_count/DEBUG': 4, 'log_count/INFO': 7, 'response_received_count': 2, 'scheduler/dequeued': 1, 'scheduler/dequeued/memory': 1, 'scheduler/enqueued': 1, 'scheduler/enqueued/memory': 1, 'start_time': datetime.datetime(2017, 4, 15, 13, 50, 54, 786607)}2017-04-15 21:50:55 [scrapy.core.engine] INFO: Spider closed (finished)G:\Scrapy_work\myfendo>

四、保存爬取到的数据

最简单存储爬取的数据的方式是使用 Feed exports:

scrapy crawl myfendos -o items.json

输出的结果:

G:\Scrapy_work\myfendo>scrapy crawl myfendos -o items.json2017-04-15 22:19:02 [scrapy.utils.log] INFO: Scrapy 1.3.3 started (bot: myfendo)2017-04-15 22:19:02 [scrapy.utils.log] INFO: Overridden settings: {'BOT_NAME': 'myfendo', 'FEED_FORMAT': 'json', 'FEED_URI': 'items.json', 'NEWSPIDER_MODULE': 'myfendo.spiders', 'ROBOTSTXT_OBEY': True, 'SPIDER_MODULES': ['myfendo.spiders']}2017-04-15 22:19:02 [scrapy.middleware] INFO: Enabled extensions:['scrapy.extensions.corestats.CoreStats', 'scrapy.extensions.telnet.TelnetConsole', 'scrapy.extensions.feedexport.FeedExporter', 'scrapy.extensions.logstats.LogStats']2017-04-15 22:19:03 [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.stats.DownloaderStats']2017-04-15 22:19:03 [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']2017-04-15 22:19:03 [scrapy.middleware] INFO: Enabled item pipelines:[]2017-04-15 22:19:03 [scrapy.core.engine] INFO: Spider opened2017-04-15 22:19:03 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)2017-04-15 22:19:03 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:60242017-04-15 22:19:03 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/robots.txt> (referer: None)2017-04-15 22:19:04 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.csdn.net/u011781521/article/details/70182815> (referer: None)2017-04-15 22:19:04 [scrapy.core.scraper] DEBUG: Scraped from <200 http://blog.csdn.net/u011781521/article/details/70182815>{'desc': ['<meta name="description" '          'content="一、Scrapy简介Scrapy是一个为了爬取网站数据，提取结构性数据而编写的应用框架。 '          '可以应用在包括数据挖掘，信息处理或存储历史数据等一系列的程序中。Scrapy 使用 '          'Twisted这个异步网络库来处理网络通讯，架构清晰，并且包含了各种中间件接口，可以灵活的完成各种需求。Scrapy吸引人的地方在于它是一个框架，任何人都可以根据需求方便的修改。它也提供">'], 'link': ['https://scrapy.org/'], 'title': ['\r\n        Python爬虫系列之----Scrapy(一)爬虫原理            \r\n        ']}2017-04-15 22:19:04 [scrapy.core.engine] INFO: Closing spider (finished)2017-04-15 22:19:04 [scrapy.extensions.feedexport] INFO: Stored json feed (1 items) in: items.json2017-04-15 22:19:04 [scrapy.statscollectors] INFO: Dumping Scrapy stats:{'downloader/request_bytes': 467, 'downloader/request_count': 2, 'downloader/request_method_count/GET': 2, 'downloader/response_bytes': 17313, 'downloader/response_count': 2, 'downloader/response_status_count/200': 2, 'finish_reason': 'finished', 'finish_time': datetime.datetime(2017, 4, 15, 14, 19, 4, 130548), 'item_scraped_count': 1, 'log_count/DEBUG': 4, 'log_count/INFO': 8, 'response_received_count': 2, 'scheduler/dequeued': 1, 'scheduler/dequeued/memory': 1, 'scheduler/enqueued': 1, 'scheduler/enqueued/memory': 1, 'start_time': datetime.datetime(2017, 4, 15, 14, 19, 3, 323475)}2017-04-15 22:19:04 [scrapy.core.engine] INFO: Spider closed (finished)G:\Scrapy_work\myfendo>

该命令将采用 JSON 格式对爬取的数据进行序列化，生成 items.json 文件。

也可以采用下面的方法保存JSON数据:

1.修改pipelines.py文件

from scrapy import signalsimport jsonimport codecsclass JsonWithEncodingCnblogsPipeline(object):    def __init__(self):        self.file = codecs.open('myitems.json', 'w', encoding='utf-8')    def process_item(self, item, spider):        line = json.dumps(dict(item), ensure_ascii=False) + "\n"        self.file.write(line)        return item    def spider_closed(self, spider):        self.file.close()

注意类名为JsonWithEncodingCnblogsPipeline哦！settings.py中会用到

2.修改settings.py，添加以下两个配置项

ITEM_PIPELINES = {    'myfendo.pipelines.JsonWithEncodingCnblogsPipeline': 300,}LOG_LEVEL = 'INFO'

然后运行爬虫:

scrapy crawl myfendos

输出结果为:

G:\Scrapy_work\myfendo>scrapy crawl myfendos2017-04-15 22:24:42 [scrapy.utils.log] INFO: Scrapy 1.3.3 started (bot: myfendo)2017-04-15 22:24:42 [scrapy.utils.log] INFO: Overridden settings: {'BOT_NAME': 'myfendo', 'LOG_LEVEL': 'INFO', 'NEWSPIDER_MODULE': 'myfendo.spiders', 'ROBOTSTXT_OBEY': True, 'SPIDER_MODULES': ['myfendo.spiders']}2017-04-15 22:24:42 [scrapy.middleware] INFO: Enabled extensions:['scrapy.extensions.corestats.CoreStats', 'scrapy.extensions.telnet.TelnetConsole', 'scrapy.extensions.logstats.LogStats']2017-04-15 22:24:42 [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.stats.DownloaderStats']2017-04-15 22:24:42 [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']2017-04-15 22:24:42 [scrapy.middleware] INFO: Enabled item pipelines:['myfendo.pipelines.JsonWithEncodingCnblogsPipeline']2017-04-15 22:24:42 [scrapy.core.engine] INFO: Spider opened2017-04-15 22:24:42 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)2017-04-15 22:24:43 [scrapy.core.engine] INFO: Closing spider (finished)2017-04-15 22:24:43 [scrapy.statscollectors] INFO: Dumping Scrapy stats:{'downloader/request_bytes': 467, 'downloader/request_count': 2, 'downloader/request_method_count/GET': 2, 'downloader/response_bytes': 17315, 'downloader/response_count': 2, 'downloader/response_status_count/200': 2, 'finish_reason': 'finished', 'finish_time': datetime.datetime(2017, 4, 15, 14, 24, 43, 434983), 'item_scraped_count': 1, 'log_count/INFO': 7, 'response_received_count': 2, 'scheduler/dequeued': 1, 'scheduler/dequeued/memory': 1, 'scheduler/enqueued': 1, 'scheduler/enqueued/memory': 1, 'start_time': datetime.datetime(2017, 4, 15, 14, 24, 42, 660934)}2017-04-15 22:24:43 [scrapy.core.engine] INFO: Spider closed (finished)G:\Scrapy_work\myfendo>

会生成一个myitems.json的文件

完整的示例: http://download.csdn.net/detail/u011781521/9815346

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