我想使用scrapy只需下载.jpg图片

Question

我有一个问题我只想下载.jpg图片。我使用了以下代码，但我发现我仍然下载.png或.gif图片。有谁可以帮助我？

#coding:utf-8
from scrapy.spiders import Spider
from scrapy.selector import Selector
from jianshu.items import JianshuItem
import scrapy
from scrapy.crawler  import  CrawlerProcess


class jiansider(Spider):
    name = "jiantu"
    allowed_domains = []
    start_urls= [
    "https://tieba.baidu.com/p/5227563995"
    ]


    def parse(self, response):

        sel = Selector(response)
        sites = sel.xpath('//div/img/@src').extract()
        item = JianshuItem()
        item['image_url'] = response.xpath('//div/img/@src').extract()
        for url in item['image_url']:



            list_photo = url.split('.')
            photo_type = list_photo[len(list_photo)-1]
            print photo_type
            if photo_type != 'jpg':
                #print url
                item['image_url'].remove(url)
                #print "delete1"


        yield item
        total_page = response.xpath('//span[@class="red"]/text()').extract()
        now_page = response.xpath('//li/span[@class="tP"]/text()').extract()
        tpa=total_page[len(total_page)-1]
        npa=now_page[len(now_page)-1]
        tpage= int(tpa)
        npage= int (npa)

        print "present page -----"
        print npage
        print "total page ------"
        print tpage
        starturls = 'https://tieba.baidu.com/p/5227563995?pn='
        if npage != tpage:
            npage = npage+1
            new_url = '%s%s'%(starturls,npage)
            print "new_url is ------------"
            print new_url       
        if new_url:
            yield  scrapy.Request(new_url,callback = self.parse)

我使用if！= .jpg来避免下载类型不是jpg的照片，但我失败了。有人可以告诉我为什么并帮助我处理它吗？