Python lxml模块的基本使用方法分析-侯体宗的博客

Python lxml模块的基本使用方法分析
Python / 管理员发布于 7年前 164

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="https:/article/link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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 etreetext = ''' <div> <ul>     <li class="item-1"><a href="https:/article/link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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="https:/article/link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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 etreetext = ''' <div> <ul>     <li class="item-1"><a href="https:/article/link1.html" rel="external nofollow" 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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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 etreetext = ''' <div> <ul>     <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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 etreetext = ''' <div> <ul>     <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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 etreetext = ''' <div> <ul>     <li class="item-1"><a>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" 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" rel="external nofollow" 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" rel="external nofollow" 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" 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

PS：这里再为大家提供几款关于xml操作的在线工具供大家参考使用：

在线XML/JSON互相转换工具：
http://tools..net.cn/code/xmljson

在线格式化XML/在线压缩XML：
http://tools..net.cn/code/xmlformat

XML在线压缩/格式化工具：
http://tools..net.cn/code/xml_format_compress

XML代码在线格式化美化工具：
http://tools..net.cn/code/xmlcodeformat

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希望本文所述对大家Python程序设计有所帮助。

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