Python中的BeautifulSoup库简要总结

时间:2022-03-29 06:26:39

一、基本元素

BeautifulSoup库是解析、遍历、维护“标签树”的功能库。

引用

 from bs4 import BeautifulSoup
 import bs4

html文档-标签树-BeautifulSoup类

 from bs4 import BeautifulSoup
soup1 = BeautifulSoup(“<html>data</html>”,”html.parser”)
soup2 = BeautifulSoup(open(“D://demo.html”),”html.parser”)

一个BeautifulSoup对象对应一个HTML/XML文档的全部内容

 1 import requests
2 from bs4 import BeautifulSoup
r = requests.get("http://python123.io/ws/demo.html")
r.text
'<html><head><title>This is a python demo page</title></head>\r\n<body>\r\n<p class="title"><b>The demo python introduces several python courses.</b></p>\r\n<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n<a href="http://www.icourse163.org/course/BIT-268001" class="py1" id="link1">Basic Python</a> and <a href="http://www.icourse163.org/course/BIT-1001870001" class="py2" id="link2">Advanced Python</a>.</p>\r\n</body></html>'
demo = r.text
soup = BeautifulSoup(demo,"html.parser")
print(soup.prettify())
<html>
<head>
<title>
This is a python demo page
</title>
</head>
<body>
<p class="title">
<b>
The demo python introduces several python courses.
</b>
</p>
<p class="course">
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
Basic Python
</a>
and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
Advanced Python
</a>
30 .
</p>
</body>
</html>

在上述代码中,一个BeautifulSoup对象对应一个HTML文档的全部内容,可查看r,demo,soup的类型

 type(r)
<class 'requests.models.Response'>
type(demo)
<class 'str'>
type(soup)
<class 'bs4.BeautifulSoup'>

BeautifulSoup库解析器

解析器 使用方法 条件
bs4的HTML解析器 BeautifulSoup(mk,’html.parser’) 安装bs4库
lxml的HTML解析器 BeautifulSoup(mk,’lxml’) 安装lxml库
lxml的XML解析器 BeautifulSoup(mk,’xml’) 安装lxml库
html5lib的解析器 BeautifulSoup(mk,’ html5lib’) 安装html5lib库

BeautifulSoup类基本元素

基本元素 说明
Tag 标签,最基本的信息组织单元,分别用<>和</>标明开头和结尾
Name 标签的名字,<p>…</p>的名字是’p’,格式:<tag>.name
Attributes 标签的属性,字典组织形式,格式:<tag>.attrs
NavigableString 标签内非属性字符串,<>…</>中字符串,格式:<tag>.string
Comment 标签内字符串的注释部分,一种特殊的Comment类型

以"http://python123.io/ws/demo.html"html文档为例,先生成soup对象(BeautifulSoup类),该文档的详细内容在※代码中可看到。

1 import requests
2 from bs4 import BeautifulSoup
r = requests.get("http://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo,"html.parser")

1、soup的标题及标签

文档中有两个a标签,直接使用soup.a只可以获得第一个a标签

 soup.title #标题
<title>This is a python demo page</title>
tag = soup.a #标签a
tag
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

2、标签名

 soup.a.name #标签a的标签名
'a'
soup.a.parent.name #标签a的父标签名
'p'
soup.a.parent.parent.name #标签a的父标签的父标签名
'body'

3、标签属性

 tag = soup.a #tag为soup中的a标签
tag.attrs #标签属性值
{'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
tag.attrs['class'] #标签'class'属性值
['py1']
tag.attrs['href'] #标签'href'属性值
'http://www.icourse163.org/course/BIT-268001'
type(tag.attrs) #标签属性类型
<class 'dict'>
type(tag) #标签类型
<class 'bs4.element.Tag'>

4、标签内非属性字符串

NavigableString可跨越多个层次,如下代码中p标签内还有b标签,但不会打印b标签,而是打印b标签内的字符串

 soup.a #标签a
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>
soup.a.string #标签a内非属性字符串
'Basic Python'
soup.p #标签p
<p class="title"><b>The demo python introduces several python courses.</b></p>
soup.p.string #标签p内非属性字符串
'The demo python introduces several python courses.'
type(soup.a.string) #标签a内非属性字符串类型
<class 'bs4.element.NavigableString'>
type(soup.p.string) #标签p内非属性字符串类型
<class 'bs4.element.NavigableString'>

5、标签内字符串的注释部分

使用<tag>.string时显示的字符串类型可能是NavigableString,也可能是Comment。

 newsoup = BeautifulSoup("<b><!-- This is a comment --></b><p>This is not a comment</p>","html.parser") #创建一个新的BeautifulSoup对象
newsoup.b.string #标签b的字符串
' This is a comment '
newsoup.p.string #标签p的字符串
'This is not a comment'
type(newsoup.b.string) #标签b的字符串类型
<class 'bs4.element.Comment'>
type(newsoup.p.string) #标签p的字符串类型
<class 'bs4.element.NavigableString'>

综上所述

<p class = "title">...</p>

标签 .<tag>

名称 .name

属性 .attrs

非属性字符串/注释 .string

 二、HTML内容的遍历方法

1、标签树的下行遍历

属性 说明
.contents 子节点的列表,将<tag>所有儿子节点存入列表
.children 子节点的迭代类型,与.contents类似,用于循环遍历儿子节点
.descendants 子孙节点的迭代类型,包含所有子孙节点,用于循环遍历

以※处的html文档为例

 import requests
from bs4 import BeautifulSoup
r = requests.get("http://python123.io/ws/demo.html")
demo = r.text
soup = BeautifulSoup(demo,"html.parser")

head标签、head标签儿子节点及body标签儿子节点

 soup.head #head标签
<head><title>This is a python demo page</title></head>
soup.head.contents #head标签儿子节点
[<title>This is a python demo page</title>]
soup.body.contents #body标签儿子节点
['\n', <p class="title"><b>The demo python introduces several python courses.</b></p>, '\n', <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>, '\n']
len(soup.body.contents) #body标签儿子节点数量
5
soup.body.contents[1] #body标签中的第二个儿子标签
<p class="title"><b>The demo python introduces several python courses.</b></p>

综上

遍历儿子节点

 for child in soup.body.children:
print(child)

遍历子孙节点

for descendant in soup.body.descendants
print(child)

2、标签树的上行遍历

属性 说明
.parent 节点的父亲标签
.parents 节点先辈标签的迭代类型,用于循环遍历先辈节点

同样的,以※处的html文档为例

 soup.title.parent #title的父标签
<head><title>This is a python demo page</title></head>
soup.html.parent #html的父标签
<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
</body></html>
soup.parent #soup的父标签

由以上代码可知,title标签的父标签为head标签,html标签是html文档的*标签,其父标签就是自己。soup是一种特殊的标签,其父标签为空。

标签树的上行遍历

 soup = BeautifulSoup(demo,"html.parser")
for parent in soup.a.parents:
if parent is None:
print(parent)
else:
print(parent.name)

3、标签树的平行遍历

平行遍历发生在同一个父节点下的各节点间

属性 说明
.next_sibling 返回按照HTML文本顺序的下一个平行节点标签
.previous_sibling 返回按照HTML文本顺序的上一个平行节点标签
.next_siblings 迭代类型,返回按照HTML文本顺序的后续所有平行节点标签
.previous_siblings 迭代类型,返回按照HTML文本顺序的前续所有平行节点标签

同样的,以※处的html文档为例

 soup.a.next_sibling #标签a的后续平行节点
' and '
soup.a.next_sibling.next_sibling #标签a后续平行节点的后续平行节点
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
soup.a.previous_sibling #标签a的前续平行节点
'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'
soup.a.previous_sibling.previous_sibling #标签a前续平行节点的前续平行节点(为空)
soup.a.parent #标签a的父亲节点
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>

遍历后续节点

 for sibling in soup.a.next_siblings:
print(sibling)

遍历前续节点

 for sibling in soup.a.previous_siblings:
print(sibling)

三、HTML的格式化和编码

prettify()方法

以※处的html文档为例

 soup.prettify()
'<html>\n <head>\n <title>\n This is a python demo page\n </title>\n </head>\n <body>\n <p class="title">\n <b>\n The demo python introduces several python courses.\n </b>\n </p>\n <p class="course">\n Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\n <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">\n Basic Python\n </a>\n and\n <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">\n Advanced Python\n </a>\n .\n </p>\n </body>\n</html>'
print(soup.prettify())
<html>
<head>
<title>
This is a python demo page
</title>
</head>
<body>
<p class="title">
<b>
The demo python introduces several python courses.
</b>
</p>
<p class="course">
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
Basic Python
</a>
and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
Advanced Python
</a>
.
</p>
</body>
</html>

编码方式为utf-8

资料来源:《Python网络爬虫与信息提取》——嵩天,北京理工大学,MOOC