发布于2022年10月15日2年前

1.BeautifulSoup简介

BeautifulSoup是一个可以从HTML或XML文件中提取数据的python库；它能够通过转换器实现惯用的文档导航、查找、修改文档的方式。

BeautifulSoup是一个基于re开发的解析库，可以提供一些强大的解析功能；使用BeautifulSoup能够提高提取数据的效率与爬虫开发效率。

2.BeautifulSoup总览

构建文档树

BeautifulSoup进行文档解析是基于文档树结构来实现的，而文档树则是由BeautifulSoup中的四个数据对象构建而成的。

文档树对象	描述
Tag	标签; 访问方式:soup.tag;属性:tag.name(标签名)，tag.attrs(标签属性)
Navigable String	可遍历字符串; 访问方式:soup.tag.string
BeautifulSoup	文档全部内容，可作为Tag对象看待; 属性:soup.name(标签名)，soup.attrs(标签属性)
Comment	标签内字符串的注释; 访问方式:soup.tag.string

import lxml
import requests
from bs4 import BeautifulSoup

html =  """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1"><!--Elsie--></a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""

#1、BeautifulSoup对象
soup = BeautifulSoup(html,'lxml')
print(type(soup))

#2、Tag对象
print(soup.head,'\n')
print(soup.head.name,'\n')
print(soup.head.attrs,'\n')
print(type(soup.head))

#3、Navigable String对象
print(soup.title.string,'\n')
print(type(soup.title.string))

#4、Comment对象
print(soup.a.string,'\n')
print(type(soup.a.string))

#5、结构化输出soup对象
print(soup.prettify())

遍历文档树

BeautifulSoup之所以将文档转为树型结构，是因为树型结构更便于对内容的遍历提取。

向下遍历方法	描述
tag.contents	tag标签子节点
tag.children	tag标签子节点，用于循环遍历子节点
tag.descendants	tag标签子孙节点，用于循环遍历子孙节点

向上遍历方法	描述
tag.parent	tag标签父节点
tag.parents	tag标签先辈节点，用于循环遍历先别节点

平行遍历方法	描述
tag.next_sibling	tag标签下一兄弟节点
tag.previous_sibling	tag标签上一兄弟节点
tag.next_siblings	tag标签后续全部兄弟节点
tag.previous_siblings	tag标签前序全部兄弟节点

import requests
import lxml
import json
from bs4 import BeautifulSoup

html =  """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1"><!--Elsie--></a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""

soup = BeautifulSoup(html,'html.parser')

#1、向下遍历
print(soup.p.contents)
print(list(soup.p.children))
print(list(soup.p.descendants))

#2、向上遍历
print(soup.p.parent.name,'\n')
for i in soup.p.parents:
    print(i.name)

#3、平行遍历
print('a_next:',soup.a.next_sibling)
for i in soup.a.next_siblings:
    print('a_nexts:',i)
print('a_previous:',soup.a.previous_sibling)
for i in soup.a.previous_siblings:
    print('a_previouss:',i)

搜索文档树

BeautifulSoup提供了许多搜索方法，能够便捷地获取我们需要的内容。

遍历方法	描述
soup.find_all( )	查找所有符合条件的标签，返回列表数据
soup.find	查找符合条件的第一个个标签，返回字符串数据
soup.tag.find_parents()	检索tag标签所有先辈节点，返回列表数据
soup.tag.find_parent()	检索tag标签父节点，返回字符串数据
soup.tag.find_next_siblings()	检索tag标签所有后续节点，返回列表数据
soup.tag.find_next_sibling()	检索tag标签下一节点，返回字符串数据
soup.tag.find_previous_siblings()	检索tag标签所有前序节点，返回列表数据
soup.tag.find_previous_sibling()	检索tag标签上一节点，返回字符串数据

需要注意的是，因为class是python的保留关键字，若要匹配标签内class的属性，需要特殊的方法，有以下两种：

在attrs属性用字典的方式进行参数传递
BeautifulSoup自带的特别关键字class_

import requests
import lxml
import json
from bs4 import BeautifulSoup

html =  """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1"><!--Elsie--></a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""

soup = BeautifulSoup(html,'html.parser')

#1、find_all( )
print(soup.find_all('a'))  #检索标签名
print(soup.find_all('a',id='link1')) #检索属性值
print(soup.find_all('a',class_='sister')) 
print(soup.find_all(text=['Elsie','Lacie']))

#2、find( )
print(soup.find('a'))
print(soup.find(id='link2'))

#3 、向上检索
print(soup.p.find_parent().name)
for i in soup.title.find_parents():
    print(i.name)
    
#4、平行检索
print(soup.head.find_next_sibling().name)
for i in soup.head.find_next_siblings():
    print(i.name)
print(soup.title.find_previous_sibling())
for i in soup.title.find_previous_siblings():
    print(i.name)

CSS选择器

BeautifulSoup选择器支持绝大部分的CSS选择器，在Tag或BeautifulSoup对象的.select( )方法中传入字符串参数，即可使用CSS选择器找到Tag。

常用HTML标签：

HTML标题：<h> </h>
HTML段落：<p> </p>
HTML链接：<a href='httts://www.baidu.com/'> this is a link </a>
HTML图像：<img src='Ai-code.jpg',width='104',height='144' />
HTML表格：<table> </table>
HTML列表：<ul> </ul>
HTML块：<div> </div>

import requests
import lxml
import json
from bs4 import BeautifulSoup

html =  """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1"><!--Elsie--></a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""

soup = BeautifulSoup(html,'html.parser')

print('标签查找:',soup.select('a'))
print('属性查找:',soup.select('a[id="link1"]'))
print('类名查找:',soup.select('.sister'))
print('id查找:',soup.select('#link1'))
print('组合查找:',soup.select('p #link1'))

爬取图片实例

import requests
from bs4 import BeautifulSoup
import os

def getUrl(url):
    try:
        read = requests.get(url)  
        read.raise_for_status()   
        read.encoding = read.apparent_encoding  
        return read.text    
    except:
        return "连接失败！"
 
def getPic(html):
    soup = BeautifulSoup(html, "html.parser")
    
    all_img = soup.find('ul').find_all('img') 
    for img in all_img:
        src = img['src']  
        img_url = src
        print(img_url)
        root = "F:/Pic/"   
        path = root + img_url.split('/')[-1]  
        print(path)
        try:
            if not os.path.exists(root):  
                os.mkdir(root)
            if not os.path.exists(path):
                read = requests.get(img_url)
                with open(path, "wb")as f:
                    f.write(read.content)
                    f.close()
                    print("文件保存成功！")
            else:
                print("文件已存在！")
        except:
            print("文件爬取失败！")
 
if __name__ == '__main__':
   html_url=getUrl("https://findicons.com/search/nature")
   getPic(html_url)

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Python BeautifulSoup简介

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