Python中的BeautifulSoup库简要总结

一、基本元素

BeautifulSoup库是解析、遍历、维护“标签树”的功能库。

引用

1 from bs4 import BeautifulSoup

1 import bs4

html文档-标签树-BeautifulSoup类

1 from bs4 import BeautifulSoup
2 soup1 = BeautifulSoup(“<html>data</html>”,”html.parser”)
3 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
 3 r = requests.get("http://python123.io/ws/demo.html")
 4 r.text
 5 '<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>'
 6 demo = r.text
 7 soup = BeautifulSoup(demo,"html.parser")
 8 print(soup.prettify())
 9 <html>
10  <head>
11   <title>
12    This is a python demo page
13   </title>
14  </head>
15  <body>
16   <p class="title">
17    <b>
18     The demo python introduces several python courses.
19    </b>
20   </p>
20   <p class="course">
22    Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
23    <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
24     Basic Python
25    </a>
26    and
27    <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
28     Advanced Python
29    </a>
30    .
31   </p>
32  </body>
33 </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

1 type(r)
2 <class 'requests.models.Response'>
3 type(demo)
4 <class 'str'>
5 type(soup)
6 <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
3 r = requests.get("http://python123.io/ws/demo.html")
4 demo = r.text
5 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

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

2、标签名

1 soup.a.name #标签a的标签名
2 'a'
3 soup.a.parent.name #标签a的父标签名
4 'p'
5 soup.a.parent.parent.name #标签a的父标签的父标签名
6 'body'

3、标签属性

 1 tag = soup.a #tag为soup中的a标签
 2 tag.attrs #标签属性值
 3 {'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
 4 tag.attrs['class'] #标签'class'属性值
 5 ['py1']
 6 tag.attrs['href'] #标签'href'属性值
 7 'http://www.icourse163.org/course/BIT-268001'
 8 type(tag.attrs) #标签属性类型
 9 <class 'dict'>
10 type(tag) #标签类型
11 <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

 1 soup.a #标签a
 2 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>
 3 soup.a.string #标签a内非属性字符串
 4 'Basic Python'
 5 soup.p #标签p
 6 <p class="title"><b>The demo python introduces several python courses.</b></p>
 7 soup.p.string #标签p内非属性字符串
 8 'The demo python introduces several python courses.'
 9 type(soup.a.string) #标签a内非属性字符串类型
10 <class 'bs4.element.NavigableString'>
11 type(soup.p.string) #标签p内非属性字符串类型
12 <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。

1 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
2 newsoup.b.string #标签b的字符串
3 ' This is a comment '
4 newsoup.p.string #标签p的字符串
5 'This is not a comment'
6 type(newsoup.b.string) #标签b的字符串类型
7 <class 'bs4.element.Comment'>
8 type(newsoup.p.string) #标签p的字符串类型
9 <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

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

head标签、head标签儿子节点及body标签儿子节点

 1 soup.head #head标签
 2 <head><title>This is a python demo page</title></head>
 3 soup.head.contents #head标签儿子节点
 4 [<title>This is a python demo page</title>]
 5 soup.body.contents #body标签儿子节点
 6 ['\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:
 7 <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']
 8 len(soup.body.contents) #body标签儿子节点数量
 9 5
10 soup.body.contents[1] #body标签中的第二个儿子标签
11 <p class="title"><b>The demo python introduces several python courses.</b></p>

综上

遍历儿子节点

1 for child in soup.body.children:
2     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

 1 soup.title.parent #title的父标签
 2 <head><title>This is a python demo page</title></head>
 3 soup.html.parent #html的父标签
 4 <html><head><title>This is a python demo page</title></head>
 5 <body>
 6 <p class="title"><b>The demo python introduces several python courses.</b></p>
 7 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
 8 <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>
 9 </body></html>
10 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文档的最高级标签，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

1 soup = BeautifulSoup(demo,"html.parser")
2 for parent in soup.a.parents:
3     if parent is None:
4         print(parent)
5     else:
6         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

 1 soup.a.next_sibling #标签a的后续平行节点
 2 ' and '
 3 soup.a.next_sibling.next_sibling #标签a后续平行节点的后续平行节点
 4 <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
 5 soup.a.previous_sibling #标签a的前续平行节点
 6 'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n' 
 7 soup.a.previous_sibling.previous_sibling #标签a前续平行节点的前续平行节点（为空）
 8 soup.a.parent #标签a的父亲节点
 9 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
10 <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

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

遍历前续节点

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

三、HTML的格式化和编码

prettify()方法