python爬虫之xpath的基本使用详解

Python  /  管理员 发布于 7年前   177

一、简介

XPath 是一门在 XML 文档中查找信息的语言。XPath 可用来在 XML 文档中对元素和属性进行遍历。XPath 是 W3C XSLT 标准的主要元素，并且 XQuery 和 XPointer 都构建于 XPath 表达之上。 

二、安装

pip3 install lxml

三、使用

1、导入

from lxml import etree

2、基本使用

from lxml import etreewb_data = """    <div>      <ul>         <li class="item-0"><a href="https:/article/link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>         <li class="item-1"><a href="https:/article/link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>         <li class="item-inactive"><a href="https:/article/link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>         <li class="item-1"><a href="https:/article/link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>         <li class="item-0"><a href="https:/article/link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>       </ul>     </div>    """html = etree.HTML(wb_data)print(html)result = etree.tostring(html)print(result.decode("utf-8"))

从下面的结果来看，我们打印机html其实就是一个python对象，etree.tostring(html)则是不全里html的基本写法，补全了缺胳膊少腿的标签。

 <Element html at 0x39e58f0><html><body><div>      <ul>         <li class="item-0"><a href="https:/article/link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>         <li class="item-1"><a href="https:/article/link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>         <li class="item-inactive"><a href="https:/article/link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>         <li class="item-1"><a href="https:/article/link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>         <li class="item-0"><a href="https:/article/link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>       </li></ul>     </div>    </body></html>

3、获取某个标签的内容(基本使用)，注意，获取a标签的所有内容，a后面就不用再加正斜杠，否则报错。

写法一

html = etree.HTML(wb_data)html_data = html.xpath('/html/body/div/ul/li/a')print(html)for i in html_data:  print(i.text)<Element html at 0x12fe4b8>first itemsecond itemthird itemfourth itemfifth item

写法二（直接在需要查找内容的标签后面加一个/text()就行）

html = etree.HTML(wb_data)html_data = html.xpath('/html/body/div/ul/li/a/text()')print(html)for i in html_data:  print(i) <Element html at 0x138e4b8>first itemsecond itemthird itemfourth itemfifth item

4、打开读取html文件

#使用parse打开html的文件html = etree.parse('test.html')html_data = html.xpath('//*')<br>#打印是一个列表，需要遍历print(html_data)for i in html_data:  print(i.text) 
html = etree.parse('test.html')html_data = etree.tostring(html,pretty_print=True)res = html_data.decode('utf-8')print(res) 打印：<div>   <ul>     <li class="item-0"><a href="https:/article/link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>     <li class="item-1"><a href="https:/article/link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >second item</a></li>     <li class="item-inactive"><a href="https:/article/link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>     <li class="item-1"><a href="https:/article/link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>     <li class="item-0"><a href="https:/article/link5.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a></li>   </ul></div>

5、打印指定路径下a标签的属性（可以通过遍历拿到某个属性的值，查找标签的内容）

html = etree.HTML(wb_data)html_data = html.xpath('/html/body/div/ul/li/a/@href')for i in html_data:  print(i)

打印：

link1.html

link2.html

link3.html

link4.html

link5.html

6、我们知道我们使用xpath拿到得都是一个个的ElementTree对象，所以如果需要查找内容的话，还需要遍历拿到数据的列表。

查到绝对路径下a标签属性等于link2.html的内容。

html = etree.HTML(wb_data)html_data = html.xpath('/html/body/div/ul/li/a[@href="https:/article/link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]/text()')print(html_data)for i in html_data:  print(i)

打印：

['second item']

second item

7、上面我们找到全部都是绝对路径（每一个都是从根开始查找），下面我们查找相对路径，例如，查找所有li标签下的a标签内容。

html = etree.HTML(wb_data)html_data = html.xpath('//li/a/text()')print(html_data)for i in html_data:  print(i)

打印：

['first item', 'second item', 'third item', 'fourth item', 'fifth item']

first item

second item

third item

fourth item

fifth item

8、上面我们使用绝对路径，查找了所有a标签的属性等于href属性值，利用的是/---绝对路径，下面我们使用相对路径，查找一下l相对路径下li标签下的a标签下的href属性的值，注意，a标签后面需要双//。

html = etree.HTML(wb_data)html_data = html.xpath('//li/a//@href')print(html_data)for i in html_data:  print(i)

打印：

['link1.html', 'link2.html', 'link3.html', 'link4.html', 'link5.html']

link1.html

link2.html

link3.html

link4.html

link5.html

9、相对路径下跟绝对路径下查特定属性的方法类似，也可以说相同。

html = etree.HTML(wb_data)html_data = html.xpath('//li/a[@href="https:/article/link2.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]')print(html_data)for i in html_data:  print(i.text)

打印：

[<Element a at 0x216e468>]

second item

10、查找最后一个li标签里的a标签的href属性

html = etree.HTML(wb_data)html_data = html.xpath('//li[last()]/a/text()')print(html_data)for i in html_data:  print(i)

打印：

['fifth item']

fifth item

11、查找倒数第二个li标签里的a标签的href属性 

html = etree.HTML(wb_data)html_data = html.xpath('//li[last()-1]/a/text()')print(html_data)for i in html_data:  print(i)

打印：

['fourth item']

fourth item

12、如果在提取某个页面的某个标签的xpath路径的话，可以如下图：

//*[@id="kw"]

解释：使用相对路径查找所有的标签，属性id等于kw的标签。

常用

#!/usr/bin/env python# -*- coding:utf-8 -*-from scrapy.selector import Selector, HtmlXPathSelectorfrom scrapy.http import HtmlResponsehtml = """<!DOCTYPE html><html>  <head lang="en">    <meta charset="UTF-8">    <title></title>  </head>  <body>    <ul>      <li class="item-"><a id='i1' href="https:/article/link.html" rel="external nofollow" rel="external nofollow" >first item</a></li>      <li class="item-0"><a id='i2' href="https:/article/llink.html" rel="external nofollow" >first item</a></li>      <li class="item-1"><a href="https:/article/llink2.html" rel="external nofollow" rel="external nofollow" >second item<span>vv</span></a></li>    </ul>    <div><a href="https:/article/llink2.html" rel="external nofollow" rel="external nofollow" >second item</a></div>  </body></html>"""response = HtmlResponse(url='http://example.com', body=html,encoding='utf-8')# hxs = HtmlXPathSelector(response)# print(hxs)# hxs = Selector(response=response).xpath('//a')# print(hxs)# hxs = Selector(response=response).xpath('//a[2]')# print(hxs)# hxs = Selector(response=response).xpath('//a[@id]')# print(hxs)# hxs = Selector(response=response).xpath('//a[@id="i1"]')# print(hxs)# hxs = Selector(response=response).xpath('//a[@href="https:/article/link.html" rel="external nofollow" rel="external nofollow" ][@id="i1"]')# print(hxs)# hxs = Selector(response=response).xpath('//a[contains(@href, "link")]')# print(hxs)# hxs = Selector(response=response).xpath('//a[starts-with(@href, "link")]')# print(hxs)# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]')# print(hxs)# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]/text()').extract()# print(hxs)# hxs = Selector(response=response).xpath('//a[re:test(@id, "i\d+")]/@href').extract()# print(hxs)# hxs = Selector(response=response).xpath('/html/body/ul/li/a/@href').extract()# print(hxs)# hxs = Selector(response=response).xpath('//body/ul/li/a/@href').extract_first()# print(hxs) # ul_list = Selector(response=response).xpath('//body/ul/li')# for item in ul_list:#   v = item.xpath('./a/span')#   # 或#   # v = item.xpath('a/span')#   # 或#   # v = item.xpath('*/a/span')#   print(v)

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。


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