Python3如何抓取网页和只抓图片？

#!/usr/bin/env python 
 
from urllib import urlretrieve 
 
def firstNonBlank(lines): 
 for eachLine in lines: 
  if not eachLine.strip(): 
   continue 
  else: 
   return eachLine 
 
def firstLast(webpage): 
 f = open(webpage) 
 lines = f.readlines() 
 f.close() 
 print firstNonBlank(lines), 
 lines.reverse() 
 print firstNonBlank(lines), 
 
def download(url='http://www',process=firstLast): 
 try: 
  retval = urlretrieve(url)[0] 
 except IOError: 
  retval = None 
 if retval: 
  process(retval) 
 
if __name__ == '__main__': 
 download() 

import urllib.request 
import socket 
import re 
import sys 
import os 
targetDir = r"C:\Users\elqstux\Desktop\pic" 
def destFile(path): 
 if not os.path.isdir(targetDir): 
  os.mkdir(targetDir) 
 pos = path.rindex('/') 
 t = os.path.join(targetDir, path[pos+1:]) 
 return t 
 
if __name__ == "__main__": 
 hostname = "http://www.douban.com" 
 req = urllib.request.Request(hostname) 
 webpage = urllib.request.urlopen(req) 
 contentBytes = webpage.read() 
 for link, t in set(re.findall(r'(http:[^\s]*?(jpg|png|gif))', str(contentBytes))): 
  print(link) 
  urllib.request.urlretrieve(link, destFile(link)) 

import urllib.request 
import socket 
import re 
import sys 
import os 
targetDir = r"H:\pic" 
def destFile(path): 
 if not os.path.isdir(targetDir): 
  os.mkdir(targetDir) 
 pos = path.rindex('/') 
 t = os.path.join(targetDir, path[pos+1:]) #会以/作为分隔 
 return t 
 
if __name__ == "__main__": 
 hostname = "http://www.douban.com/" 
 req = urllib.request.Request(hostname) 
 webpage = urllib.request.urlopen(req) 
 contentBytes = webpage.read() 
 match = re.findall(r'(http:[^\s]*?(jpg|png|gif))', str(contentBytes) )#r'(http:[^\s]*?(jpg|png|gif))'中包含两层圆括号，故有两个分组， 
               #上面会返回列表，括号中匹配的内容才会出现在列表中 
 for picname, picType in match: 
  print(picname) 
  print(picType) 
  
 
''''' 
输出： 
http://img3.douban.com/pics/blank.gif 
gif 
http://img3.douban.com/icon/g111328-1.jpg 
jpg 
http://img3.douban.com/pics/blank.gif 
gif 
http://img3.douban.com/icon/g197523-19.jpg 
jpg 
http://img3.douban.com/pics/blank.gif 
gif 
... 
'''