求教：python爬取淘宝页面的图片，网页已经爬取成功，但无法匹配到图片，不知道什么问题，是正则表达式的问题吗？

[abbrieviation]

import urllib.request
import re

'''get access to taobao'''

words="连衣裙"

keywords=urllib.request.quote(words)

#fake header
headers=("User-Agent","Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.86 Safari/537.36")
opener=urllib.request.build_opener()
opener.addheaders=[headers]
urllib.request.install_opener(opener)

'''climb the webs and corresponding pictures'''

for i in range(1,3):
url = 'http://s.taobao.com/list?&q='+keywords+'&cat=16&style=grid&seller_type=taobao&bcoffset=0&s='+str(i*60)

data=urllib.request.urlopen(url).read().decode('utf-8', 'ignore')
#此处以上均成功

pat='"pic_url":"//(.*?).jpg"'
pics=re.compile(pat).findall(data)

for j in range (0, len(pics)):
thispic=pics[j]
thispicurl="https://"+thispic
file='E:/python/练习文件/results/taobao_pictures/'+str(i)+str(j)+'.html'
urllib.request.urlretrieve( thispicurl, filename=file )