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">first item</a></li>
<li class="item-1"><a href="link2.html">second item</a></li>
<li class="item-inactive"><a href="link3.html">third item</a></li>
<li class="item-1"><a href="link4.html">fourth item</a></li>
<li class="item-0"><a href="link5.html">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">first item</a></li>
<li class="item-1"><a href="link2.html">second item</a></li>
<li class="item-inactive"><a href="link3.html">third item</a></li>
<li class="item-1"><a href="link4.html">fourth item</a></li>
<li class="item-0"><a href="link5.html">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(\'//*\')
#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">first item</a></li>
<li class="item-1"><a href="link2.html">second item</a></li>
<li class="item-inactive"><a href="link3.html">third item</a></li>
<li class="item-1"><a href="link4.html">fourth item</a></li>
<li class="item-0"><a href="link5.html">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"]/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"]\')
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。
#!/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">first item</a></li> <li class="item-0"><a id=\'i2\' href="llink.html">first item</a></li> <li class="item-1"><a href="llink2.html">second item<span>vv</span></a></li> </ul> <div><a href="llink2.html">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"][@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)