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
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pip3 install lxml
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三、使用
1、导入
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from lxml import etree
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2、基本使用
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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" ))
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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。
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< 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 >
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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
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html = etree.HTML(wb_data)
print (html)
for i in html_data:
print (i.text)
<Element html at 0x12fe4b8 >
first item
second item
third item
fourth item
fifth item
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写法二(直接在需要查找内容的标签后面加一个/text()就行)
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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
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4、打开读取html文件
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#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)
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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>
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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)
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html = etree.HTML(wb_data)
html_data = html.xpath( '/html/body/div/ul/li/a/@href' )
for i in html_data:
print (i)
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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。
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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)
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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。
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html = etree.HTML(wb_data)
html_data = html.xpath( '//li/a/text()' )
print (html_data)
for i in html_data:
print (i)
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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//。
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html = etree.HTML(wb_data)
html_data = html.xpath( '//li/a//@href' )
print (html_data)
for i in html_data:
print (i)
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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。
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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)
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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
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html = etree.HTML(wb_data)
html_data = html.xpath( '//li[last()]/a/text()' )
print (html_data)
for i in html_data:
print (i)
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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
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html = etree.HTML(wb_data)
html_data = html.xpath( '//li[last()-1]/a/text()' )
print (html_data)
for i in html_data:
print (i)
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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:
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//*[@id="kw"]
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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
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#!/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)
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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服务器之家。
原文链接:http://www.cnblogs.com/lei0213/p/7506130.html