python爬⾍之xpath的基本使⽤详解
⼀、简介
XPath 是⼀门在 XML ⽂档中查信息的语⾔。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" 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 = string(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，string(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" 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>
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:
)
<Element html at 0x12fe4b8>
first item
second item
third item
fourth item
fifth item
写法⼆（直接在需要查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
href标签怎么用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('//*')<br>#打印是⼀个列表，需要遍历
print(html_data)
for i in html_data:
)
html = etree.parse('test.html')
html_data = string(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>
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_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)
打印：
['second item']
second item
7、上⾯我们到全部都是绝对路径（每⼀个都是从根开始查），下⾯我们查相对路径，例如，查所有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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ]')
print(html_data)
for i in html_data:
)
打印：
[<Element a at 0x216e468>]
second item
10、查最后⼀个li标签⾥的a标签的href属性
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：使⽤相对路径查所有的标签，属性id等于kw的标签。
常⽤
#!/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='example', 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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