Scrapy中间件的使用

下载中间件（MiddleproDownloaderMiddleware）

• 位置：引擎和下载器之间
• 作用：批量拦截到整个工程中所有的请求和响应
• 拦截请求：
  • UA伪装
  • IP代理
• 拦截响应：
  • 篡改响应数据、响应请求

[middlewares.py] MiddleproDownloaderMiddleware类中有3个重要方法

import random
from fake_useragent import UserAgent

class MiddleproDownloaderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.
    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/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; SE 2.X MetaSr 1.0; SE 2.X MetaSr 1.0; .NET CLR 2.0.50727; SE 2.X MetaSr 1.0)",
        "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/4.0 (compatible; MSIE 7.0; Windows NT 5.1; 360SE)",
        "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"
    ]
    
    PROXY_http = [
        '153.180.102.104:80',
        '195.208.131.189:56055'
    ]
    PROXY_https = [
        '120.83.49.90:9000',
        '95.189.112.214:35508'
    ]
           

• process_request() 拦截请求
  1. 使用UA池（不推荐）

     def process_request(self, request, spider):
             # Called for each request that goes through the downloader
             # middleware.
     
             # Must either:
             # - return None: continue processing this request
             # - or return a Response object
             # - or return a Request object
             # - or raise IgnoreRequest: process_exception() methods of
             #   installed downloader middleware will be called
             """
             函数说明：拦截请求
             :param request:
             :param spider:
             :return:
             """
             # UA伪装
             request.headers['User-Agent'] = rando.chiose(self.USER_AGENT_LIST)
     
             return None
                

  2. 使用 fake-useragent 模块（推荐）

     安装模块：

     pip install fake-useragent

     def process_request(self, request, spider):
                 # Called for each request that goes through the downloader
                 # middleware.
     
                 # Must either:
                 # - return None: continue processing this request
                 # - or return a Response object
                 # - or return a Request object
                 # - or raise IgnoreRequest: process_exception() methods of
                 #   installed downloader middleware will be called
                 """
                 函数说明：拦截请求
                 :param request:
                 :param spider:
                 :return:
                 """
                 # UA伪装
                 request.headers['User-Agent'] = UserAgent().random
                

• process_response() 拦截所有的响应
  • 这里以 爬取网易新闻为例
• process_exception() 拦截异常的请求
  • 代理IP

    PROXY_http = [
        '153.180.102.104:80',
        '195.208.131.189:56055'
    ]
    PROXY_https = [
        '120.83.49.90:9000',
        '95.189.112.214:35508'
    ]
      
      	def process_exception(self, request, exception, spider):
            # Called when a download handler or a process_request()
            # (from other downloader middleware) raises an exception.
    
            # Must either:
            # - return None: continue processing this exception
            # - return a Response object: stops process_exception() chain
            # - return a Request object: stops process_exception() chain
            """
            函数说明：拦截发生异常的请求
            :param request:
            :param exception:
            :param spider:
            :return:
            """
            # 代理IP
            if request.url.split(':')[0] == 'http':
                request.meta['proxy'] = 'http://' + random.choice(self.PROXY_http)
            else:
                request.meta['proxy'] = 'https://' + random.choice(self.PROXY_https)
    
            # 请修正之后的请求对象进行重新的请求发送
            return request