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Beautiful Soup库的使用

Beautiful Soup库的安装及基本使用

Beautiful Soup 是一个可以从 HTMLXML 文件中提取数据的 Python 库。

它能够通过你喜欢的转换器实现惯用的文档导航,查找,修改文档的方式.Beautiful Soup 会帮你节省数小时甚至数天的工作时间。

安装Beautiful Soup:

pip install beautifulsoup4

Beautiful Soup使用的小例子:

>>> import requests
>>> from bs4 import BeautifulSoup

# 使用requests获取页面数据
>>> r = requests.get("https://python123.io/ws/demo.html")
>>> demo = r.text

# 使用Beautiful Soup解析页面数据
>>> soup = BeautifulSoup(demo, "html.parser")
>>> type(soup)
<class 'bs4.BeautifulSoup'>

Beautiful Soup库的基本元素

Beautiful Soup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’)pip install lxml
lxml的XML解析器BeautifulSoup(mk, ‘xml’)pip install lxml
html5lib的解析器BeautifulSoup(mk, ‘html5lib’)pip install html5lib

上面的四种解析器,各有各的优缺点,下面就介绍以下它们的优缺点,方便大家根据实际的场景选择使用那种解析器

解析器优点缺点
bs4的HTML解析器Python内置标准库,执行速度适中、文档容错能力强Python2.7.3及3.2.2之前的版本文档容错能力差
lxml的HTML解析器速度快、文档容错能力强需要安装C语言库
lxml的XML解析器速度快、唯一支持XML的解析器需要安装C语言库
html5lib的解析器最后的容错性、以浏览器的方式解析文档、生成HTML5格式的文档速度慢、不依赖外部扩展

Beautiful Soup类的基本元素

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,字典形式组织,格式:<tag>.attrs
NavigableString标签内非属性的字符串,<>…</>中的字符串,格式:<tag>.string
Comment标签内字符串的注释部分,一种特殊的Comment类型

Beautiful Soup基本元素的演示

Tag

>>> type(soup.a)
<class 'bs4.element.Tag'>
>>> soup.a
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

Name

>>> type(soup.p.name)
<class 'str'>
>>> soup.p.name  # p标签的名字
'p'
>>> soup.p.parent.name  # p标签的父亲名字
'body'

Attributes

>>> type(soup.a.attrs)
<class 'dict'>
>>> soup.a.attrs  # 获取a标签的所有属性
{'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
>>> soup.a.attrs["href"]  # 获取a标签的href属性
'http://www.icourse163.org/course/BIT-268001'
>>> soup.a.attrs["class"]  # 获取a标签的class属性
['py1']

NavigableString

>>> type(soup.p.string)
<class 'bs4.element.NavigableString'>
>>> soup.p.string
'The demo python introduces several python courses.'

Comment

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

HTML内容遍历

标签树子孙遍历常用的方法

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

实例演示:

.contents

>>> soup = BeautifulSoup(r.text, "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>]
>>> len(soup.head.contents)
1

.children

>>> soup.head.children # 迭代器类型,遍历儿子节点
<list_iterator object at 0x103df8fd0>
>>> for child in soup.head.children:
...     print(child)
...
<title>This is a python demo page</title>

.descendants

>>> soup.body.descendants # 生成器类型,方便生成迭代器,遍历子孙节点
<generator object Tag.descendants at 0x104367ad0>
>>> for child in soup.body.descendants:
...     print(child)
...
<p class="title"><b>The demo python introduces several python courses.</b></p>
<b>The demo python introduces several python courses.</b>
The demo python introduces several python courses.

...

标签树上行遍历常用的方法

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

实例演示:

.parent

>>> soup.title.parent # title标签的父标签
<head><title>This is a python demo page</title></head>
>>> soup.b.parent # b标签的父标签
<p class="title"><b>The demo python introduces several python courses.</b></p>

.parents

>>> for parent in soup.a.parents: # 输出a标签的所有先辈的名称
...     if parent is not None:
...         print(parent.name)
...
p
body
html
[document]

标签树平行遍历常用的方法

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

实例演示:

.next_sibling

>>> soup.a.next_sibling  # a标签的平行节点标签有可能会是NavigableString类型,因此,当看到这种情况的时候,不需要惊讶,可以通过类型来进行标签的筛选
' and '
>>> soup.a.next_sibling.next_sibling # a标签的第二级平行标签
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>

.previous_sibling

>>> soup.a.previous_sibling # a标签的平行节点标签有可能会是NavigableString类型,因此,当看到这种情况的时候,不需要惊讶,可以通过类型来进行标签的筛选
'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.parent # 通过查看a标签的父标签,我们可以发现,a标签的前续标签是一个NavigableString类型的数据
<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>

.next_siblings

>>> for sibling in soup.a.next_siblings:
...     print(sibling)
...
 and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>

.previous_siblings

>>> for sibling in soup.a.previous_siblings:
...     print(sibling)
...
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

基于bs4库的HTML格式输出

bs4库的prettify()方法,这个方法可以非常优美的HTML格式的代码输出出来。

此外还需要注意的一点是,bs4库会将它得到的数据全部转换为utf-8编码,因为Python3默认的编码就是utf-8,所以使用bs4库无障碍,但是若是你还是使用的Python2,则建议升级为Python3,否则就需要不断的去转换编码。

>>> import requests
>>> from bs4 import BeautifulSoup
>>> r = requests.get("https://python123.io/ws/demo.html")
>>> demo = r.text
>>> 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()) # 格式化输出全部标签
<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>
>>> print(soup.a.prettify()) # 格式化输出a标签
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
 Basic Python
</a>
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