import urllib2
import re

url = "http://u.caoadult.com/album/23157/?page=%s"
baseurl = "http://u.caoadult.com/media/photos/"

target = open("output.txt", 'w')

for i in xrange(1, 21):
    u = url % i
    urlcontent = urllib2.urlopen(u).read()
    imgurls=re.findall('img .*?src="/media/photos/(.*?)"',urlcontent)
    for imgurl in imgurls:
        print baseurl+imgurl
        target.write(baseurl+imgurl+'\n')

target.close()