Scrapy爬虫(八)：中间件的使用实例

本章将介绍最简单的中间件user-agent中间件的使用。

user-agent

user-agent是咱们模拟浏览器比较重要的参数，主要是防止爬虫被ban，前几章我们了解到在settings.py中可以设置user-agent，如：

USER_AGENT = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36'

但是这种情况还是有被禁(ban)的情况，另外我们再增加延时爬取，也可以减小被ban的风险，当然这些都是比较简单的伪装技巧，作为爬虫入门已经够用。
那么我们设置更多的user-agent来模拟浏览器下载网页数据，每次下载时随机设置一个user-agent，这样更不容易被ban。

最简单的中间件

新建一个文件middlewares.py

# -*-coding:utf-8-*-import randomfrom scrapy.downloadermiddlewares.useragent import UserAgentMiddlewareclass RotateUserAgentMiddleware(UserAgentMiddleware):    def __init__(self, user_agent=''):        self.user_agent = user_agent    def process_request(self, request, spider):        ua = random.choice(self.user_agent_list)        if ua:            # print(ua)            request.headers.setdefault('User-Agent', ua)    # the default user_agent_list composes chrome,I E,firefox,Mozilla,opera,netscape    # for more user agent strings,you can find it in http://www.useragentstring.com/pages/useragentstring.php    user_agent_list = [ \        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/22.0.1207.1 Safari/537.1" \        "Mozilla/5.0 (X11; CrOS i686 2268.111.0) AppleWebKit/536.11 (KHTML, like Gecko) Chrome/20.0.1132.57 Safari/536.11", \        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1092.0 Safari/536.6", \        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1090.0 Safari/536.6", \        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/19.77.34.5 Safari/537.1", \        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.9 Safari/536.5", \        "Mozilla/5.0 (Windows NT 6.0) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.36 Safari/536.5", \        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3", \        "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3", \        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_0) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3", \        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.0 Safari/536.3", \        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.24 (KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24", \        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.24 (KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24"    ]

settings.py中配置中间件

DOWNLOADER_MIDDLEWARES = {    'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware': None,    'douban.middlewares.RotateUserAgentMiddleware': 543,}

这样我们就设置了一个最简单的中间件到爬虫中，每次爬取的时候都会从RotateUserAgentMiddleware中随机设置一个user-agent，本章实例以增加到上章的实例中。

github地址

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• 专题概要
• 爬虫简介
• scrapy架构及原理
• imdb.cn爬虫实例
• 有限爬取深度实例
• 多个爬虫组合实例
• 爬虫数据存储实例
• 中间件的使用实例
• scrapy的调试技巧
• 爬虫总结以及扩展