编程 Python

Python lxml模块的基本使用方法分析

Posted in Python onDecember 21, 2019

本文实例讲述了Python lxml模块的基本使用方法。分享给大家供大家参考，具体如下：

1 lxml的安装

安装方式：pip install lxml

2 lxml的使用

2.1 lxml模块的入门使用

导入lxml 的 etree 库 (导入没有提示不代表不能用)

from lxml import etree

利用etree.HTML，将字符串转化为Element对象,Element对象具有xpath的方法,返回结果的列表，能够接受bytes类型的数据和str类型的数据

html = etree.HTML(text) 
ret_list = html.xpath("xpath字符串")

把转化后的element对象转化为字符串，返回bytes类型结果 etree.tostring(element)

假设我们现有如下的html字符换，尝试对他进行操作

<div> <ul> 
<li class="item-1"><a href="link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> # 注意，此处缺少一个 </li> 闭合标签 
</ul> </div>

from lxml import etree
text = ''' <div> <ul> 
    <li class="item-1"><a href="link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> 
    </ul> </div> '''
html = etree.HTML(text)
print(type(html)) 
handeled_html_str = etree.tostring(html).decode()
print(handeled_html_str)

输出为

<class 'lxml.etree._Element'>
<html><body><div> <ul>
        <li class="item-1"><a href="link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a>
        </li></ul> </div> </body></html>

可以发现，lxml确实能够把确实的标签补充完成，但是请注意lxml是人写的，很多时候由于网页不够规范，或者是lxml的bug，即使参考url地址对应的响应去提取数据，任然获取不到，这个时候我们需要使用etree.tostring的方法，观察etree到底把html转化成了什么样子，即根据转化后的html字符串去进行数据的提取。

2.2 lxml的深入练习

接下来我们继续操作，假设每个class为item-1的li标签是1条新闻数据，如何把这条新闻数据组成一个字典

from lxml import etree
text = ''' <div> <ul> 
    <li class="item-1"><a href="link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> 
    </ul> </div> '''
html = etree.HTML(text)
#获取href的列表和title的列表
href_list = html.xpath("//li[@class='item-1']/a/@href")
title_list = html.xpath("//li[@class='item-1']/a/text()")
#组装成字典
for href in href_list:
  item = {}
  item["href"] = href
  item["title"] = title_list[href_list.index(href)]
  print(item)

输出为

{'href': 'link1.html', 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}

假设在某种情况下，某个新闻的href没有，那么会怎样呢？

from lxml import etree
text = ''' <div> <ul> 
    <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> 
    </ul> </div> '''

结果是

{'href': 'link2.html', 'title': 'first item'}
{'href': 'link4.html', 'title': 'second item'}

数据的对应全部错了，这不是我们想要的，接下来通过2.3小节的学习来解决这个问题

2.3 lxml模块的进阶使用

前面我们取到属性，或者是文本的时候，返回字符串但是如果我们取到的是一个节点，返回什么呢?

返回的是element对象，可以继续使用xpath方法，对此我们可以在后面的数据提取过程中：先根据某个标签进行分组，分组之后再进行数据的提取

示例如下：

from lxml import etree
text = ''' <div> <ul> 
    <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> 
    </ul> </div> '''
html = etree.HTML(text)
li_list = html.xpath("//li[@class='item-1']")
print(li_list)

结果为：

[<Element li at 0x11106cb48>, <Element li at 0x11106cb88>, <Element li at 0x11106cbc8>]

可以发现结果是一个element对象，这个对象能够继续使用xpath方法

先根据li标签进行分组，之后再进行数据的提取

from lxml import etree
text = ''' <div> <ul> 
    <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >fifth item</a> 
    </ul> </div> '''
#根据li标签进行分组
html = etree.HTML(text)
li_list = html.xpath("//li[@class='item-1']")
#在每一组中继续进行数据的提取
for li in li_list:
  item = {}
  item["href"] = li.xpath("./a/@href")[0] if len(li.xpath("./a/@href"))>0 else None
  item["title"] = li.xpath("./a/text()")[0] if len(li.xpath("./a/text()"))>0 else None
  print(item)

结果是：

{'href': None, 'title': 'first item'}
{'href': 'link2.html', 'title': 'second item'}
{'href': 'link4.html', 'title': 'fourth item'}

前面的代码中，进行数据提取需要判断，可能某些一面不存在数据的情况，对应的可以使用三元运算符来解决

Python lxml模块的基本使用方法分析

- Author -

Dylan HU

声明：登载此文出于传递更多信息之目的，并不意味着赞同其观点或证实其描述。

Python 相关文章推荐

Python利用pyHook实现监听用户鼠标与键盘事件

Aug 21 Python

收集的几个Python小技巧分享

Nov 22 Python

python3+PyQt5实现柱状图

Apr 24 Python

利用Anaconda简单安装scrapy框架的方法

Jun 13 Python

python opencv实现图像边缘检测

Apr 29 Python

Python 读取用户指令和格式化打印实现解析

Sep 02 Python

python中有关时间日期格式转换问题

Dec 25 Python

TensorFlow查看输入节点和输出节点名称方式

Jan 04 Python

Python实现i人事自动打卡的示例代码

Jan 09 Python

TensorFlow tensor的拼接实例

Jan 19 Python

python正则表达式实例代码

Mar 03 Python

Python中相见恨晚的技巧

Apr 13 Python

python Manager 之dict KeyError问题的解决

Dec 21 #Python

tornado+celery的简单使用详解

Dec 21 #Python

Python selenium的基本使用方法分析

Dec 21 #Python

Flask框架搭建虚拟环境的步骤分析

Dec 21 #Python

Django restframework 框架认证、权限、限流用法示例

Dec 21 #Python

python支持多线程的爬虫实例

Dec 21 #Python

Python 实现try重新执行

Dec 21 #Python