scrapy 爬取图片时图片的url总是显示None

求大家帮忙看看
class DownloadimgSpider(scrapy.Spider):
name = 'downloadimg'
allowed_domains = ['sc.chinaz.com']
start_urls = ['https://sc.chinaz.com/tupian/fengjing.html']
urls = ['https://sc.chinaz.com/tupian/fengjing_%d.html'%i for i in range(2,5)]
urls_index = 0

def parse(self, response):
    for div in response.xpath('//*[@id="container"]/div'):
        img_url = div.xpath('./div/a/img/src').extract_first()
        img_url = 'https:' + str(img_url)
        item = DownloadimgItem()
        item['img_url']=img_url
        yield item

    if self.urls_index < len(self.urls):
        yield scrapy.Request(self.urls[self.urls_index], callback=self.parse)
        self.urls_index += 1

    img_url = div.xpath('./div/a/img/src').extract_first()

src前面少了 @ 改成

    img_url = div.xpath('./div/a/img/@src').extract_first()

如有帮助，望采纳！谢谢!