python 获取一个网页里的a 标签

#!/usr/bin/python
# -*- coding: utf-8 -*-
#encoding=utf-8
#Filename:urllib2-header.py
import re
import urllib2
import sys

url= "http://www.jb51.net"
send_headers = {
 'Host':'www.jb51.net',
 'User-Agent':'Mozilla/5.0 (Windows NT 6.2; rv:16.0) Gecko/20100101 Firefox/16.0',
 'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
 'Connection':'keep-alive'
}

req = urllib2.Request(url,headers=send_headers)

r = urllib2.urlopen(req)
html = r.read().replace(" ","")
urls=re.findall(r"<a.*?href=.*?<\/a>",html,re.I)
for i in urls:
  print i