1. 目标:开发轻量级爬虫(不包括需登陆的 和 Javascript异步加载的)
不需要登陆的静态网页抓取
2. 内容:
2.1 爬虫简介
2.2 简单爬虫架构
2.3 URL管理器
2.4 网页下载器(urllib2)
2.5 网页解析器(BeautifulSoup)
2.6 完整实例:爬取百度百科Python词条相关的1000个页面数据
3. 爬虫简介:一段自动抓取互联网信息的程序
爬虫价值:互联网数据,为我所用。
4. 简单爬虫架构:
运行流程:
5. URL管理器:管理待抓取URL集合 和 已抓取URL集合
- 防止重复抓取、防止循环抓取
- 实现方式:
6. 网页下载器:将互联网URL对应的网页下载到本地的工具
- 分类:
- urllib2 下载网页的方法:
1. 最简洁方法: url ===> urllib2.urlopen(url)
import urllib2 # 直接请求 response = urllib2.urlopen('http://www.baidu.com') # 获取状态码,如果是200表示获取成功 print response.getcode() # 读取内容 cont = response.read()
2. 添加data、http header: (url,data,header) ===> urllib2.Request ===> urllib2.urlopen(request)
import urllib2 # 创建Request对象 request = urllib2.Request(url) # 添加数据 request.add_data('a', '1') # 添加http的header request.add_header('User-Agent', 'Mozilla/5.0') # 发送请求获取结果 response = urllib2.urlopen(request)
3. 添加特殊情景的处理器:
import urllib2, cookielib # 创建cookie容器 cj = cookielib.CookieJar() # 创建1个opener opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cj)) # 给urllib2安装opener urllib2.install_opener(opener) # 使用带有cookie的urllib2访问网页 response = urllib2.urlopen(“http://www.baidu.com/”)
7. urllib2 实例代码演示:
# -*- coding: utf-8 -*- """ Created on Tue Feb 14 10:31:06 2017 @author: Wayne """ import urllib2, cookielib url = "http://www.baidu.com" print "the 1st method" response1 = urllib2.urlopen(url) print response1.getcode() print len(response1.read()) print "the 2nd method" request = urllib2.Request(url) request.add_header("user-agent", "Mozilla/5.0") response2 = urllib2.urlopen(request) print response2.getcode() print len(response2.read()) print "the 3rd method" cj = cookielib.CookieJar() opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cj)) response3 = urllib2.urlopen(url) print response3.getcode() print cj print response3.read()
8. 网页解析器:从网页中提取有价值数据的工具
python 的网页解析器:
结构化解析 - DOM ( Document Object Model) 树:
9. 网页解析器 - Beautiful Soup
9.1 Beautiful Soup
- Python 第三方库,用于从HTML或XML中提取数据
- 官网:http://www.crummy.com/software/BeautifulSoup
9.2 安装并测试 beautifulsoup4
- 安装:pip install beautifulsoup4
- 测试:import bs4
9.3 Beautiful Soup语法
9.4 创建 BeautifulSoup 对象
from bs4 import BeautifulSoup # 根据 HTML 网页字符串创建 BeautifulSoup 对象 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 )
9.5 搜索节点(find_all, find)
# 方法:find_all(name, attrs, string) # 查找所有标签为 a 的节点 soup.find_all('a') # 查找所有标签为 a,链接符合 /view/123.htm 形式的节点 soup.find_all('a', href='/view/123.htm') soup.find_all('a', href=re.compiler(r'/view/\d+\.htm')) # 查找所有标签为div, class为abc,文字为Python的节点 soup.find_all('div', class_='abc', string='Python')
9.6 访问节点信息
# 得到节点: <a href='1.html'>Python</a> # 获取查找到的节点的标签名称 node.name # 获取查找到的a节点的href属性 node['href'] # 获取查找到的a节点的链接文字 node.get_text()
10. BeautifulSoup 实例测试
# -*- coding: utf-8 -*- """ Created on Tue Feb 14 11:00:42 2017 @author: Wayne """ 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" >Elsie</a>, <a href="http://example.com/lacie" class="sister" >Lacie</a> and <a href="http://example.com/tillie" class="sister" >Tillie</a>; and they lived at the bottom of a well.</p> <p class="story">...</p> """ soup = BeautifulSoup(html_doc, 'html.parser', from_encoding='urf-8') print '\n## Get all the links' links = soup.find_all('a') for link in links: print link.name, link['href'], link.get_text() print '\n## Get the links include "lacie"' link_node = soup.find('a', href='http://example.com/lacie') print link_node.name, link_node['href'], link_node.get_text() print '\n## RE matching' link_node = soup.find('a', href=re.compile(r"ill")) print link_node.name, link_node['href'], link_node.get_text() print '\n## Get "P" Paragraph Text' p_node = soup.find('p', class_='title') print p_node.name, p_node.get_text()
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