根据scrapy官方文档： http://doc.scrapy.org/en/master/topic... 里面的描述，要防止scrapy被屏蔽，主要有以下几个策略。

1. 动态设置user agent
2. 禁用cookies
3. 设置延迟下载
4. 使用 Google cache
5. 使用IP地址池（ Tor project 、VPN和代理IP）
6. 使用 Crawlera

由于Google cache受国内网络的影响；Crawlera的分布式下载，不宜开展。所以本文主要从动态随机设置user agent、禁用cookies、设置延迟下载和使用代理IP这几个方式。

1、创建middlewares.py

scrapy代理IP、user agent的切换都是通过DOWNLOADER_MIDDLEWARES进行控制，下面我们创建middlewares.py文件。

[root@bogon cnblogs]# vi testspider/middlewares.py
import random
import base64
from settings import PROXIES
class RandomUserAgent(object):
  """Randomly rotate user agents based on a list of predefined ones"""
  def __init__(self, agents):
    self.agents = agents
  @classmethod
  def from_crawler(cls, crawler):
    return cls(crawler.settings.getlist('USER_AGENTS'))
  def process_request(self, request, spider):
    #print "**************************" + random.choice(self.agents)
    request.headers.setdefault('User-Agent', random.choice(self.agents))
class ProxyMiddleware(object):
  def process_request(self, request, spider):
    proxy = random.choice(PROXIES)
    if proxy['user_pass'] is not None:
      request.meta['proxy'] = "http://%s" % proxy['ip_port']
      encoded_user_pass = base64.encodestring(proxy['user_pass'])
      request.headers['Proxy-Authorization'] = 'Basic ' + encoded_user_pass
      print "**************ProxyMiddleware have pass************" + proxy['ip_port']
    else:
      print "**************ProxyMiddleware no pass************" + proxy['ip_port']
      request.meta['proxy'] = "http://%s" % proxy['ip_port']

类RandomUserAgent主要用来动态获取user agent，user agent列表USER_AGENTS在settings.py中进行配置。

类ProxyMiddleware用来切换代理，proxy列表PROXIES也是在settings.py中进行配置 。

2、修改settings.py配置USER_AGENTS和PROXIES

a)：添加USER_AGENTS

USER_AGENTS = [
  "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; AcooBrowser; .NET CLR 1.1.4322; .NET CLR 2.0.50727)",
  "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; Acoo Browser; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.0.04506)",
  "Mozilla/4.0 (compatible; MSIE 7.0; AOL 9.5; AOLBuild 4337.35; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)",
  "Mozilla/5.0 (Windows; U; MSIE 9.0; Windows NT 9.0; en-US)",
  "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 2.0.50727; Media Center PC 6.0)",
  "Mozilla/5.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 1.0.3705; .NET CLR 1.1.4322)",
  "Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.30)",
  "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN) AppleWebKit/523.15 (KHTML, like Gecko, Safari/419.3) Arora/0.3 (Change: 287 c9dfb30)",
  "Mozilla/5.0 (X11; U; Linux; en-US) AppleWebKit/527+ (KHTML, like Gecko, Safari/419.3) Arora/0.6",
  "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.2pre) Gecko/20070215 K-Ninja/2.1.1",
  "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9) Gecko/20080705 Firefox/3.0 Kapiko/3.0",
  "Mozilla/5.0 (X11; Linux i686; U;) Gecko/20070322 Kazehakase/0.4.5",
  "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.8) Gecko Fedora/1.9.0.8-1.fc10 Kazehakase/0.5.6",
  "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11",
  "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/535.20 (KHTML, like Gecko) Chrome/19.0.1036.7 Safari/535.20",
  "Opera/9.80 (Macintosh; Intel Mac OS X 10.6.8; U; fr) Presto/2.9.168 Version/11.52",
]

b)：添加代理IP设置PROXIES

PROXIES = [
  {'ip_port': '111.11.228.75:80', 'user_pass': ''},
  {'ip_port': '120.198.243.22:80', 'user_pass': ''},
  {'ip_port': '111.8.60.9:8123', 'user_pass': ''},
  {'ip_port': '101.71.27.120:80', 'user_pass': ''},
  {'ip_port': '122.96.59.104:80', 'user_pass': ''},
  {'ip_port': '122.224.249.122:8088', 'user_pass': ''},
]

代理IP可以网上搜索一下，上面的代理IP获取自：http://www.xici.net.co/。

c)：禁用cookies

COOKIES_ENABLED=False

d)：设置下载延迟

DOWNLOAD_DELAY=3

保存settings.py

3、测试

[root@bogon cnblogs]# scrapy crawl testSpider

篇外话：本文的user agent和proxy列表都是采用settings.py的方式进行设置的，实际生产中user agent和proxy有可能会经常更新，每次更改配置文件显得很笨拙也不便于管理。因而，可以根据需要保存在mysql数据库。