BeautifulSoup库的安装与使用

BeautifulSoup库的安装

Win平台：“以管理员身份运行” cmd

执行 pip install beautifulsoup4

演示HTML页面地址：http://python123.io/ws//demo.html

文件名称：demo.html

网页源代码：HTML 5.0 格式代码

BeautifulSoup库的安装小测：

 1 >>> import requests
 2 >>> r = requests.get("http://python123.io/ws//demo.html")
 3 >>> r.text
 4 '<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 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>
</body></html>'
 5 >>> demo = r.text
 6 >>> from bs4 import BeautifulSoup
 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>
21   <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>
34 >>>

Beautiful Soup库的基本元素：

Beautiful Soup库的理解：

Beautiful Soup库是解析、遍历、维护“标签树”的功能库。

<p>..</p> : 标签Tag

Beautiful Soup库的引用：

　　 from bs4 import BeautifulSoup

　　 import bs4

Beautiful Soup库解析器：

soup = BeautifulSoup ('<html>data</html>','html.parser')

BeautifulSoup类的基本元素：

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

Tag标签：

1 >>> from bs4 import BeautifulSoup
2 >>> soup = BeautifulSoup(demo,'html.parser')
3 >>> soup.title
4 <title>This is a python demo page</title>
5 >>> tag = soup.a
6 >>> tag
7 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

任何存在于HTML语法中的标签都可以用soup.<tag>访问获得当HTML文档中存在多个相同<tag>对应内容时，soup.<tag>返回第一个

Tag的name:

1 >>> from bs4 import BeautifulSoup
2 >>> soup = BeautifulSoup(demo,'html.parser')
3 >>> soup.a.name
4 'a'
5 >>> soup.a.parent.name
6 'p'
7 >>> soup.a.parent.parent.name
8 'body'
9 >>>

每个<tag>都有自己的名字，通过<tag>.name获取，字符串类型

Tag的attrs(属性)：

 1 >>> tag = soup.a
 2 >>> tag.attrs
 3 {'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
 4 >>> tag.attrs['class']
 5 ['py1']
 6 >>> tag.attrs['href']
 7 'http://www.icourse163.org/course/BIT-268001'
 8 >>> type(tag.attrs)
 9 <class 'dict'>
10 >>> type(tag)
11 <class 'bs4.element.Tag'>

一个<tag>可以有0或多个属性，字典类型

Tag的NavigableString:

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

NavigableString可以跨越多个层次

Tag的Comment：

1 >>> newsoup = BeautifulSoup("<b><!--This is a comment--></b><p>This is not a comment</p>","html.parser")
2 >>> newsoup.b.string
3 'This is a comment'
4 >>> type(newsoup.b.string)
5 <class 'bs4.element.Comment'>
6 >>> newsoup.p.string
7 'This is not a comment'
8 >>> type(newsoup.p.string)
9 <class 'bs4.element.NavigableString'>

Comment是一种特殊类型

标签<tag>

基于bs4库的HTML内容遍历方法：

HTML基本格式：

<>...</>构成了所属关系，形成了标签的树形结构

标签树的下行遍历：

BeautifulSoup类型是标签树的根节点

标签树的下行遍历

 1 >>> soup = BeautifulSoup(demo,'html.parser')
 2 >>> soup.head
 3 <head><title>This is a python demo page</title></head>
 4 >>> soup.head.contents
 5 [<title>This is a python demo page</title>]
 6 >>> soup.body.contents
 7 ['
', <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:
 8 
 9 <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>, '
']
10 >>> len(soup.body.contents)
11 >>> soup.body.contents[1]
12 <p class="title"><b>The demo python introduces several python courses.</b></p>

遍历儿子节点：

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

遍历子孙节点：

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

标签树的上行遍历：

1 soup = BeautifulSoup(demo,'html.parser')
2 for parent in soup.a.parents:           #标签树的上行遍历
3     if parent is None:
4         print(parent)
5     else:
6         print(parent.name)

遍历所有先辈节点，包括soup本身，所以要区别判断

运行结果：

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

遍历的判断：

让HTML内容更加“友好”的显示：

bs4库的prettify()方法：

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

.prettify()为HTML文本<>及其内容增加' '

.prettify()可用于标签，方法：<tag>.prettify()

1 >>> print(soup.a.prettify())
2 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
3  Basic Python
4 </a>

bs4库的编码：

bs4库将任何HTML输入都变为utf-8编码，Python 3.x默认支持编码是utf-8，解析无障碍。

1 >>> soup = BeautifulSoup("<p>中文</p>",'html.parser')
2 >>> soup.p.string
3 '中文'
4 >>> print(soup.p.prettify())
5 <p>
6  中文
7 </p>