网页解析器

1.网页解析器：从网页中提取有价值的数据。

2.python网页解析的方式：

正则表达式、html.parser（python自带）、Beautiful Soup（第三方）、lxml（python自带）.

Beautiful Soup可以使用html.parser或者lxml作为解析器

3.网页解析器就是结构化解析-DOM（Document Object Model）树

4.安装Beautiful Soup以及官网地址

pip install beautifulsoup4

http://www.crummy.com/software/BeautifulSoup/bs4/doc/

举例说明：

<a href='123.html' class='article_link'>Python </a>
节点名称：a
节点属性：href='123.html'和class='article_link'
节点内容：Python

使用BeautifulSoup解析网页,能够得到一个 BeautifulSoup 的对象,并能按照标准的缩进格式的结构输出:

#-*- coding: utf-8 -*-
from bs4 import BeautifulSoup
import re
html_doc = """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>

<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>

<p class="story">...</p>
"""
soup = BeautifulSoup(html_doc)
print(soup.prettify())

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查看输出：

<html>
 <head>
  <title>
   The Dormouse's story
  </title>
 </head>
 <body>
  <p class="title">
   <b>
    The Dormouse's story
   </b>
  </p>
  <p class="story">
   Once upon a time there were three little sisters; and their names were
   <a class="sister" href="http://example.com/elsie" id="link1">
    Elsie
   </a>
   ,
   <a class="sister" href="http://example.com/lacie" id="link2">
    Lacie
   </a>
   and
   <a class="sister" href="http://example.com/tillie" id="link3">
    Tillie
   </a>
   ;
and they lived at the bottom of a well.
  </p>
  <p class="story">
   ...
  </p>
 </body>
</html>

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代码实现：

#-*- coding: utf-8 -*-
from bs4 import BeautifulSoup
import re
html_doc = """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>

<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>

<p class="story">...</p>
"""
# 根据HTML网页字符串创建BeautifulSoup
# HTML文档字符串 #HTML解析器 #HTML文档的编码
soup = BeautifulSoup(html_doc,'html.parser',from_encoding='utf-8')

print ('-------获取所有的连接------------')
links = soup.find_all('a')
for link in links:
    print link.name, link['href'], link.get_text()

print ('-------获取lacie的连接------------')
link_nodes = soup.find_all('a', href='http://example.com/lacie')
for link_node in link_nodes:
    print link_node.name, link_node['href'], link_node.get_text()

print ('---------正则匹配----------')
link_nodes = soup.find_all('a', href=re.compile(r"ill"))
for link_node in link_nodes:
    print link_node.name, link_node['href'], link_node.get_text()

print ('---------获取P段落文字----------')

p_nodes = soup.find_all('p', class_="title")
# class_是为避免与关键字冲突
for p_node in p_nodes:
    print p_node.name, p_node.get_text()

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查看输出：

-------获取所有的连接------------
a http://example.com/elsie Elsie
a http://example.com/lacie Lacie
a http://example.com/tillie Tillie
-------获取lacie的连接------------
a http://example.com/lacie Lacie
---------正则匹配----------
a http://example.com/tillie Tillie
---------获取P段落文字----------
p The Dormouse's story

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