Python中间件_python的scrapy模块?

scrapy中间件包含两块，爬虫中间件，下载中间件，主要以下载中间件，middlewares.py修改后如下

先在setting打开中件间配置：DOWNLOADER_MIDDLEWARES = {'loadImg.middlewares.LoadimgDownloaderMiddleware': 543,}

当前文件：D:python_testscrapyProjectloadImgloadImgmiddlewares.py

from scrapy import signals
class LoadimgDownloaderMiddleware:

    #类方法：作用是返回一个下载器对象（忽略）
    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    #拦截处理所有的请求对象
    #参数：request就是拦截到的请求对象，spider爬虫文件中爬虫类实例化的对象
    #spider.类方法的变量名，获取数据
    def process_request(self, request, spider):
        print(spider.name) #name就爬虫文件的类变量
        return None

    #拦截处理所有的响应对象
    #参数：response就是拦截到的响应对象，request是被拦截到响应对象对应的唯一的一个请求对象
    def process_response(self, request, response, spider):
        return response

    #拦截和处理发生异常的请求对象
    #参数：reqeust就是拦截到的发生异常的请求对象
    def process_exception(self, request, exception, spider):
        return request # 发生异常后可以修正数据后重新发起请求

    #控制日志数据的（忽略）
    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

先在setting打开中件间配置：DOWNLOADER_MIDDLEWARES = {'loadImg.middlewares.LoadimgDownloaderMiddleware': 543,}

当前文件：D:python_testscrapyProjectloadImgloadImgmiddlewares.py

from scrapy import signals
class LoadimgDownloaderMiddleware:

      def process_request(self, request, spider):
         # request.meta['proxy'] = 'http://ip:port'
         # request.headers['User-Agent'] = 'UA值'
         # request.headers['cookie'] = 'xxx'
         print(request.url + ':请求对象拦截成功！')
         return None

      def process_response(self, request, response, spider):
          print(request.url + ':响应对象拦截成功！')
          return response

      def process_exception(self, request, exception, spider):
         print(request.url + ':发生异常的请求对象被拦截到！')       
         # request.meta['proxy'] = 'https://ip:port'
         return request  # 对请求对象进行重新发送