爬虫之数据解析

数据解析简介

数据解析：解析或提取数据，从通用爬虫获取的整张页面中，取得指定的局部数据

作用：实现聚焦爬虫
实现方式：
- 正则（相比来说麻烦一些）
- bs4（python中独有的）
- xpath（java，php，python均可使用）
- pyquery（python独有）
数据解析的通用原理是什么？
- 解析的一定是html页面的源码数据
  - 解析标签中存储的文本内容
  - 解析标签属性的属性值
- 原理：
  - 1，标签定位
  - 2，取文本或者取属性
爬虫实现的流程：
- 指定url
- 发请求
- 获取响应数据
- 数据解析
- 将解析到的数据持久化存储

正则解析

正则回顾

 单字符：
        . : 除换行以外所有字符
        [] ：[aoe] [a-w] 匹配集合中任意一个字符
        d ：数字  [0-9]
        D : 非数字
        w ：数字、字母、下划线、中文
        W : 非w
        s ：所有的空白字符包,括空格、制表符、换页符等等。等价于 [ f

	v]。
        S : 非空白
    数量修饰：
        * : 任意多次  >=0
        + : 至少1次   >=1
        ? : 可有可无  0次或者1次
        {m} ：固定m次 hello{3,}
        {m,} ：至少m次
        {m,n} ：m-n次
    边界：
        $ : 以某某结尾 
        ^ : 以某某开头
    分组：
        (ab)  
    贪婪模式： .*
    非贪婪（惰性）模式： .*?

    re.I : 忽略大小写
    re.M ：多行匹配
    re.S ：单行匹配

    re.sub(正则表达式, 替换内容, 字符串)

案例：取出段子对应的标题

需求：使用正则将http://duanziwang.com/category/%E6%90%9E%E7%AC%91%E5%9B%BE/对应的段子标题取出

import requests
import re

headers = {
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36'
}
url = 'http://duanziwang.com/category/搞笑图/'
#捕获到的是字符串形式的响应数据
page_text = requests.get(url=url,headers=headers).text

#数据解析
ex = '<div class="post-head">.*?<a href="http://duanziwang.com/d+.html">(.*?)</a></h1>'
ret = re.findall(ex,page_text,re.S)#爬虫使用正则做解析的话re.S必须要使用

#持久化存储
with open("./title.txt","a",encoding="utf-8") as f:
    for i in ret:
        f.write(f"{i}
")

bs4解析

环境安装
- pip install bs4
- pip install lxml
解析原理&实现流程
- 1，实例化一个BeautifulSoup的对象，需要将等待被解析的页面源码数据加载到该对象中
- 2，调用BeautifulSoup对象中相关的属性和方法进行标签定位和文本数据的t提取
BeautifulSoup如何实例化
- 方式1：BeautifulSoup(等待被解析的源码数据,“lxml”)，将本地存储的一张html文件中的指定数据进行解析
- 方式2：BeautifulSoup(响应数据,"lxml")，将从互联网中爬取的数据进行数据解析

常用的方法和属性

标签定位：根据标签名进行定位，只返回第一个出现的标签
- soup.标签名 返回当前源码中的第一个出现的标签名
属性定位：根据指定的属性进行对应标签的定位
- soup.find(标签名，标签属性=属性值) 只有class属性加 class_
  
  soup,find("tagName")
- soup.findall(标签名，标签属性=属性值)
选择器定位
- soup.select(".类")
  
  soup.select("#id")
- 层级选择器
  - 大于号：表示一个层级
  - 空格：表示多个层级
取文本
- 标签定位到的标签.string
  
  tag.string
  - 取出标签下直系的文本内容
- 标签定位到的标签.text
  
  tag.text
  - 取出标签下所有的文本内容
取属性
- 标签定位到的标签["字符串形式的属性名称"]
  
  tag.["attrName"]

案例：爬取小说

网址：https://www.52bqg.com/book_10508/

# 这种网站最好使用代理池
# 案例1
import requests
from bs4 import BeautifulSoup

headers = {
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36",
}
url = "https://www.52bqg.com/book_10508/"
fp = open("./九仙图.txt","w",encoding="utf-8")
page_text = requests.get(url=url,headers=headers)
page_text.encoding="GBK"
x = page_text.text
soup = BeautifulSoup(x,'lxml')
a_list = soup.select('#list a')
for i in a_list:
    title = i.string
    a_href = 'https://www.52bqg.com/book_10508/' + i['href']
    page_text_a = requests.get(url=a_href,headers=headers)
    page_text_a.encoding="GBK"
    f = page_text_a.text
    a_soup = BeautifulSoup(f,'lxml')
    div_tag = a_soup.find('div',id='content')
    content = div_tag.text
    fp.write("
" + title + "
" + content + "
")
    print(title,"下载完成")
fp.close()

网址：http://www.balingtxt.com/txtml_84980.html

# 案例2
import requests
from bs4 import BeautifulSoup

headers = {
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36",
}
url = "http://www.balingtxt.com/txtml_84980.html"
page_text = requests.get(url=url,headers=headers)
page_text.encoding="utf-8"
page_text = page_text.text
menu_soup = BeautifulSoup(page_text,"lxml")
a_lst = menu_soup.select("#yulan > li > a")
fp = open("./天命相师.txt","w",encoding="utf-8")
for i in a_lst:
    title = i.string
    a_url = i["href"]
    new_text = requests.get(url=a_url,headers=headers)
    new_text.encoding="utf-8"
    new_text = new_text.text
    contcent_soup = BeautifulSoup(new_text,"lxml")
    content = contcent_soup.find("div",class_="book_content").text
    fp.write(f"{title}
{content}
")
    print(f"{title}  下载完成！")
fp.close()

图片数据的爬取

基于`requests`

import requests

headers = {
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36",
}
url = "http://a0.att.hudong.com/78/52/01200000123847134434529793168.jpg"
img_data = requests.get(url=url,headers=headers).content	# 返回的是二进制类型的数据
with open("./tiger1.jpg","wb") as f:
    f.write(img_data)

content 返回的是二进制数据，如爬取图片，音频，视频

基于`urllib`

from urllib import request
url = "http://a0.att.hudong.com/78/52/01200000123847134434529793168.jpg"
ret = request.urlretrieve(url=url,filename="./trger2.jpg")
print(ret)

requests和urllib的区别就是能否实现UA伪装

Xpath解析

环境安装
- pip install lxml
解析原理&流程
- 实例化一个etree的对象，且将被解析的页面源码数据加载到该对象中
- 使用etree对象中的xpath方法结合者不同形式的xpath表达式进行标签定位和数据的提取
实例化对象
- etree.parse("文件路径")：将本地存储的html文件中的数据加载到实例化好etree对象中
- etree.HTML("page_text")：将网络上爬取的数据加载到其中
XPath表达式
- 标签定位
  - 最左侧的/：必须冲根节点定位标签（几乎不用）
  - 非最左侧的/：表示一个层级
  - 最左侧的//：可以从任意位置进行指定标签的定位
  - 非最左侧的//：表示多个层级（最常用）
  - 属性定位："//tagName[@attrName='value']"
    
    "//标签名[@属性名称=‘属性值’]"
  - 索引定位："//标签名[索引]" # 索引值从1开始，为了方便寻址
  - //div[contains(@class,'ng')] # 所有的div中，class属性值中包含ng的
  - //div[start-with(@calss,'ta')] # 所有的div中，class属性值以'ta'开头的
- 取文本
  - tree.xpath的返回值之列表，取值时需要索引
  - /text()：取直系的文本
  - //text()：取出所有的文本
- 取属性
  - /@属性名称

案例：Xpath下载图片

需求：使用Xpath解析图片地址和名称且将图片进行下载保存到本地
- http://pic.netbian.com/4kfengjing/
- 爬取高清大图

import requests
import os
from lxml import etree
from urllib import request
headers = {
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36'
}

dirName = "imglibs"		# 存储图片的文件夹名字
if not os.path.exists(dirName):
    os.mkdir(dirName)		# 没有该文件夹就创建
page_url = "http://pic.netbian.com/4kfengjing/index_%d.html"
for page_num in range(1,10):		# 全站数据爬取，根据自己情况选择爬取的页码数
    if page_num == 1:
        url = "http://pic.netbian.com/4kfengjing/"
    else:
        url = format(page_url%page_num)
    page_text = requests.get(url=url,headers=headers).text
    # 数据解析
    tree = etree.HTML(page_text)	# 实例化一个etree对象
    img_lst = tree.xpath('//div[@class="slist"]/ul/li/a')	# 返回一个a标签的列表
    for i in img_lst:
        img_href = "http://pic.netbian.com" + i.xpath("./@href")[0]		# 路径拼接，找到大图页的地址
        img_text = requests.get(url=img_href,headers=headers).text
        new_tree = etree.HTML(img_text)		# 实例化一个新的etree对象
        img_list = new_tree.xpath('//a[@id="img"]/img')[0]		# 找到图片的img标签对象
        img_src = "http://pic.netbian.com" + img_list.xpath('./@src')[0]	# 拼接高清大图的地址
        img_alt = img_list.xpath('./@alt')[0].encode('iso-8859-1').decode('GBK')	# 找到图片的名字
        filepath = "./" + dirName + "/" + img_alt + ".jpg"  # 加.jpg后缀
        request.urlretrieve(img_src,filename=filepath)		# 持久化存储
        print(img_alt,"下载成功！")
print("Over!")

pyquery解析

安装
- pip install pyquery
引用
- from pyquery import PyQuery as pq
简介
- pyquery是jQuery的一个专供python使用的HTML解析的库，类似于bs4

使用方法

初始化方法

from pyquery import PyQuery as pq
doc =pq(html) #解析html字符串
doc =pq("http://news.baidu.com/") #解析网页
doc =pq("./a.html") #解析html 文本

基本CSS选择器

from pyquery import PyQuery as pq
html = '''
    <div id="wrap">
        <ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''
doc = pq(html)
print doc("#wrap .s_from link")

运行结果：

<link href="http://asda.com">asdadasdad12312</link>
<link href="http://asda1.com">asdadasdad12312</link>
<link href="http://asda2.com">asdadasdad12312</link>

查找子元素

from pyquery import PyQuery as pq
html = '''
    <div id="wrap">
        <ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''
#查找子元素
doc = pq(html)
items=doc("#wrap")
print(items)
print("类型为:%s"%type(items))
link = items.find('.s_from')
print(link)
link = items.children()
print(link)

运行结果：

<div id="wrap">
        <ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
类型为:<class 'pyquery.pyquery.PyQuery'>
<ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
    
<ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>

查找父元素

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
items=doc(".s_from")
print(items)
#查找父元素
parent_href=items.parent()
print(parent_href)

运行结果：

<ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
</ul>
    
<div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link href="http://asda.com">asdadasdad12312</link>
            <link href="http://asda1.com">asdadasdad12312</link>
            <link href="http://asda2.com">asdadasdad12312</link>
        </ul>
</div>

parent可以查找出外层标签包括的内容，与之类似的还有parents,可以获取所有外层节点。

查找兄弟元素

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com">asdadasdad12312</link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
items=doc("link.active1.a123")
print(items)
#查找兄弟元素
siblings_href=items.siblings()
print(siblings_href)

运行结果：

<link class="active1 a123" href="http://asda.com">asdadasdad12312</link>
            
<link class="active2" href="http://asda1.com">asdadasdad12312</link>
<link class="movie1" href="http://asda2.com">asdadasdad12312</link>

根据运行结果可以看出，siblings 返回了同级的其他标签

结论：子元素查找，父元素查找，兄弟元素查找，这些方法返回的结果类型都是pyquery类型，可以针对结果再次进行选择

遍历查找结果

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com">asdadasdad12312</link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print(it)

运行结果：

<link class="active1 a123" href="http://asda.com">asdadasdad12312</link>
            
<link class="active2" href="http://asda1.com">asdadasdad12312</link>
            
<link class="movie1" href="http://asda2.com">asdadasdad12312</link>

获取属性信息

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com">asdadasdad12312</link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print(it.attr('href'))
    print(it.attr.href)

运行结果：

http://asda.com
http://asda.com
http://asda1.com
http://asda1.com
http://asda2.com
http://asda2.com

获取文本

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com">asdadasdad12312</link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print(it.text())

运行结果：

asdadasdad12312
asdadasdad12312
asdadasdad12312

获取HTML信息

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com"><a>asdadasdad12312</a></link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print(it.html())

运行结果：

<a>asdadasdad12312</a>
asdadasdad12312
asdadasdad12312

常用DOM操作

添加，移除class标签

addClass
removeClass

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com"><a>asdadasdad12312</a></link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print("添加:%s"%it.addClass('active1'))
    print("移除:%s"%it.removeClass('active1'))

运行结果：

添加:<link class="active1 a123" href="http://asda.com"><a>asdadasdad12312</a></link>
            
移除:<link class="a123" href="http://asda.com"><a>asdadasdad12312</a></link>
            
添加:<link class="active2 active1" href="http://asda1.com">asdadasdad12312</link>
            
移除:<link class="active2" href="http://asda1.com">asdadasdad12312</link>
            
添加:<link class="movie1 active1" href="http://asda2.com">asdadasdad12312</link>
        
移除:<link class="movie1" href="http://asda2.com">asdadasdad12312</link>

需要注意的是已经存在的class标签不会继续添加

attr 为获取/修改属性 css 添加style属性

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com"><a>asdadasdad12312</a></link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link").items()
for it in its:
    print("修改:%s"%it.attr('class','active'))
    print("添加:%s"%it.css('font-size','14px'))

修改:<link class="active" href="http://asda.com"><a>asdadasdad12312</a></link>
            
添加:<link class="active" href="http://asda.com" style="font-size: 14px"><a>asdadasdad12312</a></link>
            
修改:<link class="active" href="http://asda1.com">asdadasdad12312</link>
            
添加:<link class="active" href="http://asda1.com" style="font-size: 14px">asdadasdad12312</link>
            
修改:<link class="active" href="http://asda2.com">asdadasdad12312</link>
        
添加:<link class="active" href="http://asda2.com" style="font-size: 14px">asdadasdad12312</link>

attr css操作直接修改对象的

remove

remove 移除标签

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com"><a>asdadasdad12312</a></link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("div")
print('移除前获取文本结果:
%s'%its.text())
it=its.remove('ul')
print('移除后获取文本结果:
%s'%it.text())

运行结果：

移除前获取文本结果:
hello nihao
asdasd
asdadasdad12312
asdadasdad12312
asdadasdad12312
移除后获取文本结果:
hello nihao

其他DOM方法参考：

http://pyquery.readthedocs.io/en/latest/api.html

伪类选择器

from pyquery import PyQuery as pq
html = '''
    <div href="wrap">
        hello nihao
        <ul class="s_from">
            asdasd
            <link class='active1 a123' href="http://asda.com"><a>helloasdadasdad12312</a></link>
            <link class='active2' href="http://asda1.com">asdadasdad12312</link>
            <link class='movie1' href="http://asda2.com">asdadasdad12312</link>
        </ul>
    </div>
'''

doc = pq(html)
its=doc("link:first-child")
print('第一个标签:%s'%its)
its=doc("link:last-child")
print('最后一个标签:%s'%its)
its=doc("link:nth-child(2)")
print('第二个标签:%s'%its)
its=doc("link:gt(0)") #从零开始
print("获取0以后的标签:%s"%its)
its=doc("link:nth-child(2n-1)")
print("获取奇数标签:%s"%its)
its=doc("link:contains('hello')")
print("获取文本包含hello的标签:%s"%its)

运行结果：

第一个标签:<link class="active1 a123" href="http://asda.com"><a>helloasdadasdad12312</a></link>
            
最后一个标签:<link class="movie1" href="http://asda2.com">asdadasdad12312</link>
        
第二个标签:<link class="active2" href="http://asda1.com">asdadasdad12312</link>
            
获取0以后的标签:<link class="active2" href="http://asda1.com">asdadasdad12312</link>
            <link class="movie1" href="http://asda2.com">asdadasdad12312</link>
        
获取奇数标签:<link class="active1 a123" href="http://asda.com"><a>helloasdadasdad12312</a></link>
            <link class="movie1" href="http://asda2.com">asdadasdad12312</link>
        
获取文本包含hello的标签:<link class="active1 a123" href="http://asda.com"><a>helloasdadasdad12312</a></link>

相关阅读:
datagrid
SQL语句
 JavaScript事件
 DOM和BOM
JavaScript基础知识
 css
网络编程常识
 集合框架
 多线程常识
 面向对象常识
原文地址：https://www.cnblogs.com/Golanguage/p/12522203.html

爬虫之数据解析

数据解析简介

正则解析

正则回顾

案例：取出段子对应的标题

bs4解析

常用的方法和属性

案例：爬取小说

图片数据的爬取

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Xpath解析

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pyquery解析

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基于`requests`

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