python 爬多页贴吧的图片

#!/usr/bin/pythonimport reimport urllibdef getHtml(url):    x=0    for i in range(1,5):        print i        new_link = re.sub('pn=\d+','pn=%d'%i, url, re.S)        page = urllib.urlopen(new_link)        html=page.read()        reg = r'src="(.*?\.jpg)" size'        imgre=re.compile(reg)        imglist=re.findall(imgre,html)        for imgurl  in imglist:            urllib.urlretrieve(imgurl,'%s.jpg'%x)            x=x+1html = getHtml("https://tieba.baidu.com/p/5308010085?pn=1")