Python爬虫教程四：数据清洗-xpath表达式

xpath表达式：我们可以先将 HTML文件转换成 XML文档，然后用 XPath 查找 HTML 节点或元素。

我们需要安装lxml模块来支持xpath的操作。

from lxml import etree

一、转换特定html对象

方法一：etree.HTML()

解析字符串形式html成了我们需要的html对象

#解析字符串形式html
text ='''
<div>
    <ul>
         <li class="item-0"><a href="link1.html">张三</a></li>
         <li class="item-1"><a href="link2.html">李四</a></li>
         <li class="item-inactive"><a href="link3.html">王五</a></li>
         <li class="item-1"><a href="link4.html">赵六</a></li>
         <li class="item-0"><a href="link5.html">老七</a> 
     </ul>
 </div>
'''

from lxml import etree

#etree.HTML()将字符串解析成了特殊的html对象
html=etree.HTML(text)   # <class 'lxml.etree._Element'>
#将html对象转成字符串
result=etree.tostring(html,encoding="utf-8").decode()

print(result)

方法二：etree.parse()

解析本地html成了我们需要的html对象

from lxml import etree 

#获取本地html文档
html=etree.parse(r"hello.html")    # <class 'lxml.etree._ElementTree'>
print(type(html))
result=etree.tostring(html,encoding="utf-8").decode()

print(result)

二、html.xpath()获取标签内容

result1=html.xpath("//a")  #获取所有a标签
result2=html.xpath("//li/a[@href='link2.html']")   #获取指定属性的标签
result3=html.xpath("//li/a/@href")  #获取标签的属性
result4=html.xpath("//li[last()-1]/a")   #获取倒数第二个li元素下a的内容

print(result1[-2].text) #.text获取标签内容
print(result3[0].tag) #.tag表示获取标签名

更多xpath用法，请查看下面教程：

三、实例：爬取美女图片

import os
import requests
from lxml import etree

# https://loutoushe.com/page/366   1-366页

class Spider:
    def __init__(self,begin,end):
        self.beginPage=begin
        self.endPage=end
        self.url="https://loutoushe.com/page/"
        self.BASE_DIR = "C:/Users/Administrator/Desktop/Pic/"

    # 构造url
    def beauty_girl_Spider(self):
        for page in range(self.beginPage,self.endPage+1):
            pageUrl=self.url+str(page)
            self.load_page(pageUrl)

    # 爬取页面文章链接
    def load_page(self,pageUrl):
        res = requests.get(pageUrl)
        # 将获取到的str类型结果，转为Html类型，再通过xpath找出要的连接
        html = etree.HTML(res.text)
        links = html.xpath('//div[@class="post-inner"]/div/a/@href')
        for i in links:
            self.load_detial_page(i)

    # 爬取帖子详情页，获得图片的链接
    def load_detial_page(self,detail_pageUrl):
        detail = requests.get(detail_pageUrl)
        detail_html = etree.HTML(detail.text)
        title = detail_html.xpath("//title")[0].text
        pictures = detail_html.xpath('//div[@class="swiper-slide"]/img/@data-src')
        #创建图片集的名字创建相应的目录
        dirctory = self.BASE_DIR + title
        os.mkdir(dirctory)
        #遍历图片链接，下载图片
        num=len(pictures)
        for i in range(num):
            print(f"正在下载{title},第{i+1}张.....")
            self.load_picture(dirctory, pictures[i])

    # 通过图片所在链接，爬取图片并保存图片到本地：
    def load_picture(self,dictory, pic_link):
        pic_name = pic_link.split('/')[-1]
        path = f"{dictory}/{pic_name}"  # 保存地址
        pic = requests.get(pic_link)
        file = open(path, "wb")
        file.write(pic.content)  # 下载图片

if __name__ == '__main__':
    spider=Spider(5,6) #实例化图片爬虫对象，爬第5到第6页
    spider.beauty_girl_Spider()