#!/usr/bin/python3

form scrapy.http import Request

main_urls = response.css()                              # 获取主页面url单独在paser函数中

for chird_url in main_urls:                              # 从主页面中获取单个chird_url

      yield Request(url=child_url,callback=self.child_handle)    

# Request去下载chird_url，并通过回调函数把下载好的页面给self.child_handle去解析处理

# self.child_handle 为具体页面进行提取值，没有括号，调用twisted框架

next_url = response.css()

yield Request(url=next_url,callback=self.parse)

 from urllib import parse

 url = parse.urljoin(response.url, response.urll)            # reponse.url获取当前访问的url

yield Request(url=parse.urljoin(response.url, child_url), meta={'img_url': img_url}, callback=self.child_page)

response.meta.get('img_url', '')