简单爬虫架构
动态运行流程
URL管理器的作用
URL管理器的3种实现方式
网页下载器的作用
Python网页下载器的种类
urllib2下载网页的3种方法
网页解析器的作用
Python的几种网页解析器
结构化解析依赖DOM树
Beautiful Soup语法
代码举例：
1.创建Beautiful Soup对象
from bs4 import BeautifulSoup soup = BeautifulSoup(
html_doc, #HTML文档字符串
'heml.parser', #HTML解析器
from_encoding='utf-8' #HTML文档的编码
)
2.find_all find方法的使用
3.访问节点信息
4.Beautiful Soup处理html文档举例
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, #HTML文档字符串
'html.parser', #HTML解析器
from_encoding='utf-8' #HTML文档的编码
) 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tillie的连接')
link_node = soup.find('a',href='http://example.com/tillie')
print(link_node.name,link_node['href'],link_node.get_text()) print('正则表达式匹配')
link_node2 = soup.find('a',href=re.compile(r'lsi'))
print(link_node2.name,link_node2['href'],link_node2.get_text()) print('获取P段落文字')
p_node = soup.find('p',class_='title')
print(p_node.name,p_node.get_text())
控制台输出：
1 获取所有的连接
2 a http://example.com/elsie Elsie
3 a http://example.com/lacie Lacie
4 a http://example.com/tillie Tillie
5 获取tillie的连接
6 a http://example.com/tillie Tillie
7 正则表达式匹配
8 a http://example.com/elsie Elsie
9 获取P段落文字
10 p The Dormouse's story
更高级的爬虫还会涉及到“需登陆、验证码、Ajax、服务器防爬虫、多线程、分布式”等情况
