什么是user-agent？
用户代理，服务器识别用户的操作系统，浏览器类型和渲染引擎，不同浏览器的user-agent是不同的
如何随机更改user-agent？
1. 在setting中添加user-agent列表
# setting： # 随机更换user-agent # USER_AGENT_LIST = [‘zspider/0.9-dev http://feedback.redkolibri.com/‘, # ‘Xaldon_WebSpider/2.0.b1‘, # ‘Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) Speedy Spider (http://www.entireweb.com/about/search_tech/speedy_spider/)‘, # ‘Mozilla/5.0 (compatible; Speedy Spider; http://www.entireweb.com/about/search_tech/speedy_spider/)‘, # ‘Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) AddSugarSpiderBot www.idealobserver.com‘, # ]
2. 在download_middleware中导入user-agent列表，每次列表中取得一个值
__author__ = ‘beimenchuixue‘
__blog__ = ‘http://www.cnblogs.com/2bjiujiu/‘
from random import choice
class RandomUserAgentMiddleware(object):
def __init__(self, agent_list):
super(RandomUserAgentMiddleware, self).__init__()
self.agent_list = agent_list
@classmethod
def from_crawler(cls, crawler):
# 获取USER_AGENT_LIST列表
o = crawler.settings[‘USER_AGENT_LIST‘]
return cls(o)
def process_request(self, request, spider):
if self.agent_list:
# 随机取得一个值
random_user_agent = choice(self.agent_list)
# 设置User-Agent值
request.headers.setdefault(b‘User-Agent‘, random_user_agent)
3. setting中注册download_middleware，把原生的置为None
DOWNLOADER_MIDDLEWARES = {
‘scrapy.downloadermiddlewares.useragent.UserAgentMiddleware‘: None,
‘JobBole.middlewares.RandomUserAgentMiddleware‘: 400,
}
download_middleware类有什么用？
他是介于request和response中的钩子框架，用来全局修改request和response
还有哪些更改随机user-agent方法？
scrapy-fake-useragent -- Githup直接搜索
原文：http://www.cnblogs.com/2bjiujiu/p/7368002.html