爬虫调度端：启动爬虫，停止爬虫，监视爬虫运行情况
URL管理器：对将要爬取的和已经爬取过的URL进行管理；可取出带爬取的URL，将其传送给“网页下载器”
网页下载器：将URL指定的网页下载，存储成一个字符串，在传送给“网页解析器”
网页解析器：解析网页可解析出①有价值的数据②另一方面，每个网页都包含有指向其他网页的URL，解析出来后可补充进“URL管理器”
网页解析器——Beautiful Soup-语法：
例如以下代码：
对应的代码：
1、创建BeautifulSoap对象
2、搜索节点（find_all,find）
3、访问节点信息
# -*- 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,'html.parser', from_encoding='utf-8')#(文档字符串，解析器，指定编码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_node = soup.find('a', href='http://example.com/lacie')#text='Lacie' print link_node.name,link_node['href'],link_node.get_text() print('正则匹配') link_node = soup.find('a', href=re.compile(r'ill')) print link_node.name,link_node['href'],link.get_text() print('获取p段落文字:') p_node = soup.find('p', class_='title')#class_ print p_node.name, p_node.get_text()