python爬虫之xpath的基本使用
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。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#!/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)