Python爬虫程序设计ppt课件.ppt

Python爬虫程序设计ppt课件.ppt

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1、4.2scrapy中查找HTML元素(1)在前面我们已经知道使用BeautifulSoup能查找HTML中的元素,scrapy中也有强大的查找HTML元素的功能,那就是使用xpath方法。xpath方法使用XPath语法,比BeautifulSoup的select要灵活而且速度快。例4-2-1:使用xpath查找HTML中的元素fromscrapy.selectorimportSelectorhtmlText='''HarryPotter29.99<

2、/book>LearningXML39.95'''selector=Selector(text=htmlText)print(type(selector));print(selector)s=selector.xpath("//title")print(type(s))print(s)程序结果:class'scrapy.selector.unified.Selector'>

3、l>[,](1)fromscrapy.selectorimportSelector从scrapy中引入Selector类,这个类就是选择查找类。(2)sel

4、ector=Selector(text=htmlText)使用htmlText的文字建立Selector类,就是装载HTML文档,文档装载后就形成一个Selector对象,就可以使用xpath查找元素。(3)print(type(selector)可看到selector是一个类型为scrapy.selector.unified.Selector,这个类型是一个有xpath方法的类型。((4)s=selector.xpath("//title")这个方法在文档中查找所有的的元素,其中"//"表示文档中的任何位置。一般地:selector.xpath("//tagName")</p><p>5、表示在权文档中搜索<tagName>的tags,形成一个Selector的列表。(5)print(type(s))由于<title>有两个元素,因此我们看到这是一个scrapy.selector.unified.SelectorList类,类似scrapy.selector.unified.Selector的列表。(6)print(s)我们看到s包含两个Selector对象,一个是<Selectorxpath='//title'data='<titlelang="eng">HarryPotter'>,另外一个是由此可见一般selector搜索一个的HTML元素的方法是:selector.xpath("//tagName")在装载HTML文档后selector=Selector(text=htmlText)得到的selector是对应全文档顶层的元素的,其中"//"表示全文档搜索,结果是一个Selector的列表,哪怕只有一个元素也成一个列表,例如:se

7、lector.xpath("//body")搜索到元素,结果是一个Selector的列表,包含一个Selector元素;selector.xpath("//title")搜索到两个元素,结果是Selector的列表,包含2个Selector元素;selector.xpath("//book")搜索到两个<book>元素,结果是Selector的列表,包含2个Selector元素;4.2scrapy中查找HTML元素(2</p> </div> <div class="mt-3 bg-white"> <div class="d-lg-block d-none px-3 px-lg-4 py-3 border-bottom text-center font-18"> 当前文档最多预览五页,下载文档查看全文 </div> <div class="detail-fixed-feature d-none d-lg-block" id="detailFixedFeatureBox"> <div class="px-3 px-lg-4 py-3 d-flex align-items-center justify-content-between fixed-feature-box" id="detailFixedFeature"> <div class="d-lg-flex d-none align-items-center"> <div> <a class="btn btn-outline-danger article-state" href="javascript:;" data-id="59415363" data-code="438274" data-title="Python爬虫程序设计ppt课件.ppt"> <span>侵权申诉</span> </a> <button type="button" class="btn btn-outline-secondary with-light ml-2" data-toggle="modal" data-target="#reportModal" data-id="59415363"><span>举报</span></button> </div> <nav class="d-flex align-items-center 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