python爬虫之xpath的基本使用
转发：https://www.cnblogs.com/lei0213/p/7506130.html
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 |
三、使用
1、导入
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from lxml import etree |
2、基本使用
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from lxml import etreewb_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。
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<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
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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 itemsecond itemthird itemfourth itemfifth item |
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 itemsecond itemthird itemfourth itemfifth item |
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">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）
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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)打印：link1.htmllink2.htmllink3.htmllink4.htmllink5.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"]/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。
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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)打印：['first item', 'second item', 'third item', 'fourth item', 'fifth item']first itemsecond itemthird itemfourth itemfifth 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)打印：['link1.html', 'link2.html', 'link3.html', 'link4.html', 'link5.html']link1.htmllink2.htmllink3.htmllink4.htmllink5.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"]')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
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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)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)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, "id+")]')
# print(hxs)
# hxs = Selector(response=response).xpath('//a[re:test(@id, "id+")]/text()').extract()
# print(hxs)
# hxs = Selector(response=response).xpath('//a[re:test(@id, "id+")]/@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)