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：

 >>> 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)

 >>> 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>