Python之lxml模块的etree类的使用
前言：
有关xptah语法可在W3school中查看或者在上一篇博客查看
- lxml的安装与etree类的导入
- 将html字符串转化为Element对象，且elment对象的方法
- element对象的xptah方法
1.lxml模块的安装
安装方式：在终端cmd下利用pip命令安装即可（保证网络畅通）
pip install lxml
2.element对象
element对象是xpath语法的使用对象，element对象可由html字符串转化
-
利用etree.HTML()将html字符串转化为element对象 ,
from lxml import etree MyStr = '''<meta name="baidu-site-verification" content="cZdR4xxR7RxmM4zE" /> <meta http-equiv="Pragma" content="no-cache"> <meta http-equiv="Expires" content="Sun, 6 Mar 2005 01:00:00 GMT"> ''' HtmlElement = etree.HTML(MyStr) print(type(HtmlElement)) #<class 'lxml.etree._Element'> -
将element对象转化为字符串
etree的tostring方法可以将element转化为二进制类型。故需要用encoding属性指定编码方法，否则可能会造成乱码。
且此方法会使原来不规则的html字符串补全为规则的html
HtmlStr=etree.tostring(HtmlElement,encoding="utf-8").decode() print(HtmlStr)输出：
<html><head><meta name="baidu-site-verification" content="cZdR4xxR7RxmM4zE"/> <meta http-equiv="Pragma" content="no-cache"/> <meta http-equiv="Expires" content="Sun, 6 Mar 2005 01:00:00 GMT"/> </head></html>
3.element对象的xpath方法
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")
-
如果xpath取的标签的属性，则返回字符串的列表
#取MyStr中link标签的href属性 from lxml import etree MyStr = '''<meta name="baidu-site-verification" content="cZdR4xxR7RxmM4zE" /> <meta http-equiv="Pragma" content="no-cache"> <meta http-equiv="Expires" content="Sun, 6 Mar 2005 01:00:00 GMT"> <link rel="apple-touch-icon" href="https://img3.doubanio.com/f/movie/d59b2715fdea4968a450ee5f6c95c7d7a2030065/pics/movie/apple-touch-icon.png"> <link href="https://img3.doubanio.com/f/shire/bf61b1fa02f564a4a8f809da7c7179b883a56146/css/douban.css" rel="stylesheet" type="text/css"> <link href="https://img3.doubanio.com/f/shire/ae3f5a3e3085968370b1fc63afcecb22d3284848/css/separation/_all.css" rel="stylesheet" type="text/css"> <link href="https://img3.doubanio.com/f/movie/8864d3756094f5272d3c93e30ee2e324665855b0/css/movie/base/init.css" rel="stylesheet"> <script type="text/javascript">var _head_start = new Date();</script> <script type="text/javascript" src="https://img3.doubanio.com/f/movie/0495cb173e298c28593766009c7b0a953246c5b5/js/movie/lib/jquery.js"></script> <script type="text/javascript" src="https://img3.doubanio.com/f/shire/92c148e64e4f81dc6fad7f3355308ee8cacecd92/js/douban.js"></script> <script type="text/javascript" src="https://img3.doubanio.com/f/shire/0efdc63b77f895eaf85281fb0e44d435c6239a3f/js/separation/_all.js"> ''' HtmlElement = etree.HTML(MyStr) EleList = HtmlElement.xpath("//link/@href") # 这样匹配列表中的每个元素都是字符串 print(EleList)输出：
['https://img3.doubanio.com/f/movie/d59b2715fdea4968a450ee5f6c95c7d7a2030065/pics/movie/apple-touch-icon.png', 'https://img3.doubanio.com/f/shire/bf61b1fa02f564a4a8f809da7c7179b883a56146/css/douban.css', 'https://img3.doubanio.com/f/shire/ae3f5a3e3085968370b1fc63afcecb22d3284848/css/separation/_all.css', 'https://img3.doubanio.com/f/movie/8864d3756094f5272d3c93e30ee2e324665855b0/css/movie/base/init.css'] -
如果xpath取标签，则返回element元素的列表
from lxml import etree MyStr = '''<meta name="baidu-site-verification" content="cZdR4xxR7RxmM4zE" /> <meta http-equiv="Pragma" content="no-cache"> <meta http-equiv="Expires" content="Sun, 6 Mar 2005 01:00:00 GMT"> <link rel="apple-touch-icon" href="https://img3.doubanio.com/f/movie/d59b2715fdea4968a450ee5f6c95c7d7a2030065/pics/movie/apple-touch-icon.png"> <link href="https://img3.doubanio.com/f/shire/bf61b1fa02f564a4a8f809da7c7179b883a56146/css/douban.css" rel="stylesheet" type="text/css"> <link href="https://img3.doubanio.com/f/shire/ae3f5a3e3085968370b1fc63afcecb22d3284848/css/separation/_all.css" rel="stylesheet" type="text/css"> <link href="https://img3.doubanio.com/f/movie/8864d3756094f5272d3c93e30ee2e324665855b0/css/movie/base/init.css" rel="stylesheet"> <script type="text/javascript">var _head_start = new Date();</script> <script type="text/javascript" src="https://img3.doubanio.com/f/movie/0495cb173e298c28593766009c7b0a953246c5b5/js/movie/lib/jquery.js"></script> <script type="text/javascript" src="https://img3.doubanio.com/f/shire/92c148e64e4f81dc6fad7f3355308ee8cacecd92/js/douban.js"></script> <script type="text/javascript" src="https://img3.doubanio.com/f/shire/0efdc63b77f895eaf85281fb0e44d435c6239a3f/js/separation/_all.js"> ''' HtmlElement = etree.HTML(MyStr) EleList = HtmlElement.xpath("//link[@ href]") # 这样匹配列表中的每个元素都是element元素 print(EleList)输出：
[<Element link at 0xb2e7d8>, <Element link at 0xb2e7b0>, <Element link at 0xb2e788>, <Element link at 0xb2e760>]
4.补充
**lxml的高阶使用：**当提取标签的多种属性时，可以分组提取相应的标签，在对每个标签进行处理即可，这样可防止有些标签没有相应的属性，导致信息列表对应错误
剩下的都是xpath语法的使用了，只需深入了解xpath语法即可