python 正则获取html中的值

# -*- coding: utf-8 -*-from BeautifulSoup import BeautifulSoup import redef 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&nbsp;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)