BeautifulSoup库入门

Beautiful Soup库是解析、遍历、维护“标签树”的功能库

Beautiful Soup库，也叫beautifulsoup4 或bs4约定引用方式如下，即主要是用BeautifulSoup类

from bs4 import BeautifulSoup
import bs4

一 Beautiful Soup库解析器

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

         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

二 BeautifulSoup类的基本元素

<p class=“title”> … </p>

       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

2.1 Tag标签：最基本的信息组织单元，分别用<>和</>标明开头和结尾

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

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>

2.2 Tag的name（名字）：标签的名字，<p>…</p>的名字是'p'，格式：<tag>.name

每个<tag>都有自己的名字，通过<tag>.name获取，字符串类型

>>> soup.a.name
'a'
>>> soup.a.parent.name
'p'
>>> soup.a.parent.parent.name
'body'

2.3 Tag的attrs（属性）：标签的属性，字典形式组织，格式：<tag>.attrs

一个<tag>可以有0或多个属性，字典类型

>>> 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'>
>>>

2.4 Tag的NavigableString：标签内非属性字符串，<>…</>中字符串，格式：<tag>.string

NavigableString可以跨越多个层次

>>> 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'>

2.5 Tag的Comment：标签内字符串的注释部分，一种特殊的Comment类型

Comment是一种特殊类型

>>> newsoup = BeautifulSoup("<b><!--This is a comment--></b><p>This is not a commment</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 commment'
>>> type(newsoup.p.string)
<class 'bs4.element.NavigableString'>

三基于bs4库的HTML内容遍历方法

<>…</>构成了所属关系，形成了标签的树形结构

3.1 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

>>> 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>

for child in soup.body.children:
     print(child)   遍历儿子节点
for child in soup.body.descendants:
     print(child)   遍历子孙节点

3.2 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

>>> soup.title.parent
<head><title>This is a python demo page</title></head>
>>> soup.html.parent
<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>
>>> soup.parent
>>>

>>> soup = BeautifulSoup(demo,"html.parser")
>>> for parent in soup.a.parents:
	if parent is None:
		print(parent)
	else:
		print(parent.name)

		
p
body
html
[document]

遍历所有先辈节点，包括soup本身，所以要区别判断

3.3 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

for sibling in soup.a.next_sibling:
      print(sibling)     遍历后续节点
for sibling in soup.a.previous_sibling:
      print(sibling)     遍历前续节点

总结：

BeautifulSoup 中文文档BeautifulSoup文档

本篇文章参考https://www.crummy.com/software/BeautifulSoup/bs4/doc/index.zh.html

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