python爬虫之xpath的基本使用详解


Posted in Python onApril 18, 2018

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 etree
wb_data = """
    <div>
      <ul>
         <li class="item-0"><a href="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

         <li class="item-1"><a href="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="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

         <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

         <li class="item-0"><a href="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="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

         <li class="item-1"><a href="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="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

         <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

         <li class="item-0"><a href="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 item

second item

third item

fourth item

fifth 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 item

second item

third item

fourth item

fifth 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="link1.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >first item</a></li>

     <li class="item-1"><a href="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="link3.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >third item</a></li>

     <li class="item-1"><a href="link4.html" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fourth item</a></li>

     <li class="item-0"><a href="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="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="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。

python爬虫之xpath的基本使用详解

常用

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from scrapy.selector import Selector, HtmlXPathSelector
from scrapy.http import HtmlResponse
html = """<!DOCTYPE html>
<html>
  <head lang="en">
    <meta charset="UTF-8">
    <title></title>
  </head>
  <body>
    <ul>
      <li class="item-"><a id='i1' href="link.html" rel="external nofollow" rel="external nofollow" >first item</a></li>
      <li class="item-0"><a id='i2' href="llink.html" rel="external nofollow" >first item</a></li>
      <li class="item-1"><a href="llink2.html" rel="external nofollow" rel="external nofollow" >second item<span>vv</span></a></li>
    </ul>
    <div><a href="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="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三水点靠木。

Python 相关文章推荐
本地文件上传到七牛云服务器示例(七牛云存储)
Jan 11 Python
python映射列表实例分析
Jan 26 Python
Python编程实现蚁群算法详解
Nov 13 Python
Python实现获取汉字偏旁部首的方法示例【测试可用】
Dec 18 Python
Python I/O与进程的详细讲解
Mar 08 Python
python区块及区块链的开发详解
Jul 03 Python
Python 日期区间处理 (本周本月上周上月...)
Aug 08 Python
使用Python内置模块与函数进行不同进制的数的转换
Apr 26 Python
Python3批量创建Crowd用户并分配组
May 20 Python
python中tab键是什么意思
Jun 18 Python
python boto和boto3操作bucket的示例
Oct 30 Python
python 破解加密zip文件的密码
Apr 22 Python
基于python list对象中嵌套元组使用sort时的排序方法
Apr 18 #Python
python购物车程序简单代码
Apr 18 #Python
python list元素为tuple时的排序方法
Apr 18 #Python
详谈Python中列表list,元祖tuple和numpy中的array区别
Apr 18 #Python
Python3实现购物车功能
Apr 18 #Python
Python numpy 点数组去重的实例
Apr 18 #Python
对numpy中轴与维度的理解
Apr 18 #Python
You might like
php 方便水印和缩略图的图形类
2009/05/21 PHP
vs中通过剪切板循环来循环粘贴不同内容
2011/04/30 PHP
js宝典学习笔记(上)
2007/01/10 Javascript
baidu博客的编辑友情链接的新的层窗口!经典~支持【FF】
2007/02/09 Javascript
Draggable Elements 元素拖拽功能实现代码
2011/03/30 Javascript
uploadify在Firefox下丢失session问题的解决方法
2013/08/07 Javascript
简洁Ajax函数处理(示例代码)
2013/11/15 Javascript
JS获取计算机mac地址以及IP的实现方法
2014/01/08 Javascript
JavaScript前端图片加载管理器imagepool使用详解
2014/12/29 Javascript
基于jquery步骤进度条源码分享
2015/11/12 Javascript
javascript基础语法学习笔记
2016/01/04 Javascript
详解javascript new的运行机制
2016/01/26 Javascript
JS组件系列之Bootstrap table表格组件神器【二、父子表和行列调序】
2016/05/10 Javascript
js当前页面登录注册框,固定div,底层阴影的实例代码
2016/10/04 Javascript
jQuery Ajax 实现在html页面实时显示用户登录状态
2016/12/30 Javascript
微信小程序 radio单选框组件详解及实例代码
2017/01/10 Javascript
Angular2学习教程之组件中的DOM操作详解
2017/05/28 Javascript
Vue.js上下滚动加载组件的实例代码
2017/07/17 Javascript
JS实现简单表格排序操作示例
2017/10/07 Javascript
angularjs实现天气预报功能
2020/06/16 Javascript
基于jQuery的$.getScript方法去加载javaScript文档解析
2017/11/08 jQuery
详解Angular6.0使用路由步骤(共7步)
2018/06/29 Javascript
微信小程序使用map组件实现解析经纬度功能示例
2019/01/22 Javascript
小程序根据手机机型设置自定义底部导航距离
2019/06/04 Javascript
如何解决vue在ios微信&quot;复制链接&quot;功能问题
2020/03/26 Javascript
谈谈Python进行验证码识别的一些想法
2016/01/25 Python
Python 稀疏矩阵-sparse 存储和转换
2017/05/27 Python
python 异或加密字符串的实例
2018/10/14 Python
详解Python 中sys.stdin.readline()的用法
2019/09/12 Python
利用Python pandas对Excel进行合并的方法示例
2020/11/04 Python
CSS3 函数技巧 用css 实现js实现的事情(clac Counters Tooltip)
2017/08/15 HTML / CSS
html5之Canvas路径绘图、坐标变换应用实例
2012/12/26 HTML / CSS
精油和天然健康美容产品:Art Naturals
2018/01/27 全球购物
机械制造毕业生求职信
2014/03/03 职场文书
网络舆情信息简报
2015/07/21 职场文书
大学入学感言
2015/08/01 职场文书