网络爬虫_BeautifulSoup库入门

一、Beautiful Soup库的基本元素

1.Beautiful Soup库的理解

　　　　　　　　　 　　<p>..</p>: 标签：Tag
			<p> p指的是标签的名字， Name成对出现
			<p class="title">...</p>
			属性Attributes0个或多个（由键值对构成）

2.Beautiful Soup库的引用

            引用方式
			from bs4 import BeautifulSoup
			
			使用方法
			from bs4 import BeautifulSoup
			1. soup = BeautifulSoup("<html>data<html>", "html.parser")
			2. soup = BeautifulSoup(open("D://demo.html"), "html.parser")
			BeautifulSoup对应一个HTML/XML文档的全部内容。

4.Beautiful Soup库解析器

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

分类　　

			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

5.Beautiful Soup类基本元素

<p class=“title”> … </p>

分类　　

    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

6.具体使用代码

1. 回顾demo.html

	import requests
	url2 = "http://python123.io/ws/demo.html"
	r = requests.get(url2)
	demo = r.text
	print(demo)
	打印输出
		# print(demo)
			<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>

2. Tag 标签

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
import requests

url = "http://python123.io/ws/demo.html"
r = requests.get(url)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
print(soup.title)
tag = soup.a
print(tag)
	打印输出
		# print(soup.title)
			<title>This is a python demo page</title>
		# print(tag)
			<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>

3. Tag的name（名字）

Name 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

from bs4 import BeautifulSoup
		import requests
		url2 = "http://python123.io/ws/demo.html"
		r = requests.get(url2)
		demo = r.text
		soup = BeautifulSoup(demo, "html.parser")
		print(soup.a.name)
		print(soup.a.parent.name)
		print(soup.a.parent.parent.name)
	
	打印输出
		#	print(soup.a.name)
				'a'
		# print(soup.a.parent.name)
				'p'
		# print(soup.a.parent.parent.name)
				'body'

4. Tag的attrs（属性）

Attributes 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

from bs4 import BeautifulSoup
import requests
url2 = "http://python123.io/ws/demo.html"
r = requests.get(url2)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
tag = soup.a
print(tag.attrs)
print(tag.attrs['class'])
print(tag.attrs['href'])
print(type(tag.attrs))
print(type(tag))
打印输出
			# print(tag.attrs)
				{'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
			# print(tag.attrs['class'])
				['py1']
			#	print(tag.attrs['href'])
				http://www.icourse163.org/course/BIT-268001
			# print(type(tag.attrs))
				<class 'dict'>
		  # print(type(tag))
				<class 'bs4.element.Tag'>

5. Tag的NavigableString　

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

from bs4 import BeautifulSoup
import requests
url2 = "http://python123.io/ws/demo.html"
r = requests.get(url2)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
soup.a
print(soup.a.string)
print(soup.p)
print(soup.p.string)
print(type(soup.p.string))
打印输出
		#	print(soup.a.string)
			Basic Python
		  # print(soup.p)
		  	<p class="title"><b>The demo python introduces several python courses.</b></p>
		  # print(soup.p.string)
		  	The demo python introduces several python courses.
		  # print(type(soup.p.string))
				<class 'bs4.element.NavigableString'>

6. Tag的Comment

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

from bs4 import BeautifulSoup
import requests
demo = "<b><!--This is a commet--></b><p>This is not a comment</p>"
newsoup = BeautifulSoup(demo, "html.parser")
print(newsoup.b.string)
print(newsoup.p.string)
print(type(newsoup.p.string))
	
	打印输出
		# print(newsoup.b.string)
			This is a commet
	  # print(newsoup.p.string)
	  	This is not a comment
	  # print(type(newsoup.p.string))
			<class 'bs4.element.NavigableString'>

二、基于bs4库的HTML内容遍历方法

1.回顾demo.html

import requests
url = "http://python123.io/ws/demo.html"
r = requests.get(url)
demo = r.text
print(demo)

输出的demo内容（HTML基本格式）

<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>

2.标签树的三种遍历方法

3. 标签树的下行遍历

3.1) 下行遍历的属性 BeautifulSoup类型是标签树的根节点

   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

3.2）下行遍历代码

import requests
from bs4 import BeautifulSoup
url = "http://python123.io/ws/demo.html"
r = requests.get(url)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
print(soup.head)
print(soup.head.contents)
print(soup.body.contents)
print(len(soup.body.contents)) # 打印孩子节点的个数
print(soup.body.contents[1]) # 打印第一个孩子节点
打印输出
# print(soup.head)
<head><title>This is a python demo page</title></head>

# print(soup.head.contents)
[<title>This is a python demo page</title>]

# print(soup.body.contents)
['
', <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>, '
']

# print(len(soup.body.contents))
5

# print(soup.body.contents[1]) 
<p class="title"><b>The demo python introduces several python courses.</b></p>

3.3）循环遍历

# 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)

4. 标签树的上行遍历　

4.1) 上行遍历的属性

  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

4.2）上行遍历代码

import requests
from bs4 import BeautifulSoup
url = "http://python123.io/ws/demo.html"
r = requests.get(url)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
print(soup.title.parent)
print(soup.html.parent) # html 是HTML文本的最高级标签，所以其父亲是他自己
print(soup.parent) # soup是一种特殊的标签，soup的父亲为空

打印输出
# print(soup.title.parent)
<head><title>This is a python demo page</title></head>

# print(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>

# print(soup.parent)
None

4.3) 循环遍历遍历所有先辈节点，包括soup本身，所以要区别判断

for parent in soup.a.parents:
            if parent is None:
                        print(parent)
            else
                        print(parent.name)

5. 标签树的平行遍历　

5.1) 平行遍历属性

     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_sibli             迭代类型，返回按照HTML文本顺序的前续所有平行节点标签

5.2) 平行遍历解释

　　平行遍历发生在同一个父节点下的各节点间

5.3) 平行遍历代码

import requests
from bs4 import BeautifulSoup
url = "http://python123.io/ws/demo.html"
r = requests.get(url)
demo = r.text
soup = BeautifulSoup(demo, "html.parser")
print(soup.a.next_sibling)
print(soup.a.next_sibling.next_sibling)
print(soup.a.previous_sibling)

打印输出
# print(soup.a.next_sibling) 
and 
# print(soup.a.next_sibling.next_sibling)
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
# print(soup.a.previous_sibling)
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

5.4) 循环遍历

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

6. 标签树的三种遍历总结

三、基于bs4库的HTML格式输出

1. bs4库的prettify()方法

.prettify()为HTML文本<>及其内容增加更加' '
.prettify()可用于标签，方法：<tag>.prettify()

让HTML内容更加“友好”的显示

 1 import requests
 2 from bs4 import BeautifulSoup
 3 url = "http://python123.io/ws/demo.html"
 4 r = requests.get(url)
 5 demo = r.text
 6 soup = BeautifulSoup(demo, "html.parser")
 7 print(demo)
 8 print(soup.prettify())
 9 print(soup.a.prettify())
10 
11 打印输出
12 #print(demo)
13 <html><head><title>This is a python demo page</title></head>
14 <body>
15 <p class="title"><b>The demo python introduces several python courses.</b></p>
16 <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
17 <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>
18 </body></html>
19 
20 #print(soup.prettify())
21 <html>
22  <head>
23   <title>
24    This is a python demo page
25   </title>
26  </head>
27  <body>
28   <p class="title">
29    <b>
30     The demo python introduces several python courses.
31    </b>
32   </p>
33   <p class="course">
34    Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
35    <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
36     Basic Python
37    </a>
38    and
39    <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
40     Advanced Python
41    </a>
42    .
43   </p>
44  </body>
45 </html>
46 
47 #print(soup.a.prettify())
48 <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
49  Basic Python
50 </a>

prettify()方法

2. bs4库的编码

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

from bs4 import BeautifulSoup
soup = BeautifulSoup("<p>中文</p>","html.parser")
print(soup.p.string)
print(soup.p.prettify())

打印输出
# print(soup.p.string)
中文

# print(soup.p.prettify())
<p>
 中文
</p>

RRR

本人计算机小白一枚，对编程有浓厚兴趣，在此贴出自己的计算机学习历程，还有很多不足，望多多指教！读书后发现好多的内容与具体专业有偏差，没来得及完成，虽然“有时间我就会做...”是人生最大的谎言，但有时间我会继续搞定未完成的内容，有始有终，兴趣使然！