python 正则获取html中的值

# -*- coding: utf-8 -*-
from BeautifulSoup import BeautifulSoup
import re

def get_timestamp(html):
soup = BeautifulSoup(html)
authi_elems = soup.findAll('div', { 'class': 'authi' })
for authi_elem in authi_elems:
date_elem = authi_elem.find('span', title=re.compile(r'20\d{2}-\d+-\d+\s\d{2}:\d{2}:\d{2}'))
print date_elem.get('title')

if __name__ == '__main__':
html = """
<div class="authi">
<img class="authicn vm" id="" src="static/image/common/online_member.gif" />
<em id="">发表于 <span title="2013-4-2 08:30:11">4 天前</span></em>
<span class="pipe">|</span><a href=>倒序浏览</a>
<div style="float:right;position:relative;top:-6px;"><ul>
<li style="float: left; width: 130px; height: 24px;"><wb:follow-button uid="" type="gray_2" width="136" height="24"></wb:follow-button></li>
<li style=" float:left; width: 160px; height: 24px;"></li>
</ul></div></div>
"""

get_timestamp(html)