BeautifulSoup库的安装与使用

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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：
>>> import requests
>>> 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
>>> from bs4 import BeautifulSoup
>>> 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>
   .
  </p>
 </body>
</html>
>>>
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：

>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup(demo,\'html.parser\')
>>> soup.title
<title>This is a python demo page</title>
>>> tag = soup.a
>>> tag
<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:

>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup(demo,\'html.parser\')
>>> soup.a.name
\'a\'
>>> soup.a.parent.name
\'p\'
>>> soup.a.parent.parent.name
\'body\'
>>>

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)：

>>> tag = soup.a
>>> tag.attrs
{\'href\': \'http://www.icourse163.org/course/BIT-268001\', \'class\': [\'py1\'], \'id\': \'link1\'}
>>> tag.attrs[\'class\']
[\'py1\']
>>> tag.attrs[\'href\']
\'http://www.icourse163.org/course/BIT-268001\'
>>> type(tag.attrs)
<class \'dict\'>
>>> type(tag)
<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：

>>> newsoup = BeautifulSoup("<b><!--This is a comment--></b><p>This is not a comment</p>","html.parser")
>>> newsoup.b.string
\'This is a comment\'
>>> type(newsoup.b.string)
<class \'bs4.element.Comment\'>
>>> newsoup.p.string
\'This is not a comment\'
>>> type(newsoup.p.string)
<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

>>> soup = BeautifulSoup(demo,\'html.parser\')
>>> soup.head
<head><title>This is a python demo page</title></head>
>>> soup.head.contents
[<title>This is a python demo page</title>]
>>> soup.body.contents
[\'\\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)
5
>>> soup.body.contents[1]
<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：
 
soup = BeautifulSoup(demo,\'html.parser\')
for parent in soup.a.parents:           #标签树的上行遍历
    if parent is None:
        print(parent)
    else:
        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：
>>> import requests
>>> r = requests.get("http://python123.io/ws//demo.html")
>>> demo = r.text
>>> demo
\'<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>\'
>>> soup = BeautifulSoup(demo,\'html.parser\')
>>> 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>

.prettify()为HTML文本<>及其内容增加\'\\n\'

.prettify()可用于标签，方法：<tag>.prettify()

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

>>> soup = BeautifulSoup("<p>中文</p>",\'html.parser\')
>>> soup.p.string
\'中文\'
>>> print(soup.p.prettify())
<p>
 中文
</p>

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