middlewares.py 文件源码

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
        user_agents = crawler.settings.get('USER_AGENT_CHOICES', [])

        if not user_agents:
            raise NotConfigured("USER_AGENT_CHOICES not set or empty")

        o = cls(user_agents)
        crawler.signals.connect(o.spider_opened, signal=signals.spider_opened)
        return o