Python Xpath的解析，应用

目录

• 1. Xpath解析库介绍:
  • 2. xpath语法
  • 3. xpath代码演示
  • 4. 豆瓣案例

1. Xpath解析库介绍:

# Xpath解析库介绍: 
	数据解析的过程中使用过正则表达式, 但正则表达式想要进准匹配难度较高, 一旦正则表达式书写错误, 匹配的数据也会出错. 
	网页由三部分组成: HTML, Css, JavaScript, HTML页面标签存在层级关系, 即DOM树, 在获取目 标数据时可以根据网页层次关系定位标签, 再获取标签的文本或属性.
        
# xpath解析库解析数据原理: 
1. 根据网页DOM树定位节点标签 
2. 获取节点标签的正文文本或属性值

# xpath安装, 初体验 --> 使用步骤: 
1.xpath安装: pip install lxml 
2.requests模块爬取糗事百科热门的标题: 
    
import requests 
from lxml import etree 

url = 'https://www.qiushibaike.com/' 
headers = { "User-Agent":'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.142 Safari/537.36' }
res = requests.get(url=url, headers=headers) 
#实例化对象
tree = etree.HTML(res.text) 
#解析数据
title_lst = tree.xpath('//ul/li/div/a/text()') 
for item in title_lst: 
    print(item) 
    
3.xpath使用步骤: 
from lxml import etree
tree = etree.HTML(res.text) 
tree = etree.parse(res.html, etree.HTMLParse()) # 示例如下, 了解内容 tag_or_attr = tree.xpath('xpath表达式')

2. xpath语法

# xpath语法: 
1.常用规则: 
	1. nodename: 节点名定位 
	2. //: 从当前节点选取子孙节点 
	3. /: 从当前节点选取直接子节点 
	4. nodename[@attribute="..."] 根据属性定位标签 '//div[@class="ui-main"]' 
	5. @attributename: 获取属性 
	6. text(): 获取文本 
2.属性匹配两种情况: 多属性匹配 & 单属性多值匹配 
	2.1 多属性匹配 示例: tree.xpath('//div[@class="item" and @name="test"]/text()') 
	2.2 单属性多值匹配 示例: tree.xpath('//div[contains(@class, "dc")]/text()') 
3.按序选择: 
	3.1 索引定位: 从1开始(牢记， 牢记， 牢记) 
	3.2 last()函数 
	3.3 position()函数 ---代表几个以内>,<  位置

3. xpath代码演示

from lxml import etree

# 1.实例化一个etree对象
# tree = etree.HTML('文本数据')    # 解析直接从网络上爬取内容
# reel = etree.parse('文本数据',etree.HTMLParser())   # 解析本地的HTML文本
reel = etree.parse('./test.html',etree.HTMLParser())   # 解析本地的HTML文本

#2.调用 xpath 表达式定位标签及获取其属性与文本
#2.1根据节点定位

title = reel.xpath('//title/text()')   #xpath匹配出来是一个列表
# print(title)

# 3. 定位id为007的标签，去直接文本
div_oo7 = reel.xpath('//div[@id="007"]/text()')
# print(div_oo7)

div_008 = reel.xpath('//div[@id=007]//text()')
# print(div_008)

# 4.获取节点的属性值
a_tag = reel.xpath('//a/@href')
# print(a_tag)

# 5.多属性匹配和单属性多值匹配
# 多属性匹配
div_009 = reel.xpath('//div[@class="c1" and @name="laoda"]/text()')
# print(div_009)

# 单属性多值匹配
div_010 = reel.xpath('//div[contains(@class,"c3")]/text()')
# print(div_010)

#6、按序匹配
div_011 = reel.xpath('//div[@class="divtag"]/ul/li/text()')
# print(div_011)

div_012 = reel.xpath('//div[@class="divtag"]/ul/li[4]/text()')
# print(div_012)

# div_013 = reel.xpath('//div[@class="divtag"]/ul/li[last()-1]/text()')
# print(div_013)

div_014 = reel.xpath('//div[@class="divtag"]/ul/li[position()<4]/text()')
print(div_014)

4. 豆瓣案例

import requests
from lxml import etree
url = 'https://movie.douban.com/chart'
headers = {
    'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36'
}
res = requests.get(url=url,headers=headers)
tree = etree.HTML(res.text)
ret = tree.xpath('//div[@class="pl2"]')
for i in ret:
    title = i.xpath('./a//text()')
    title_full = ''
    for j in title:
        c = j.replace('\n','').replace(' ','')
        title_full += c
    author = i.xpath('./p//text()')
    pj = i.xpath('./div/span[2]/text()')
    pf = i.xpath('./div/span[3]/text()')
    print(title_full)
    print(author[0])
    print(pj[0])
    print(pf[0])