python 正则分组获取html中匹配值

import re

html = """
<form action="/thirdparty-tpsend-transfer" style="display: none;" id="transfer_form">
<input name="tid" id="form_transfer_id">
<input name="num" id="form_transfer_num">
<input type="hidden" name="__hash__" value="e25fa899c26e9c8b54e6f5e2c73bf65b_546782153d0ccd5501f5c4ddedb71ba1" />
</form>

"""

p = re.compile('name="__hash__" value="(\w+)" />')
print p.findall(html)

#['e25fa899c26e9c8b54e6f5e2c73bf65b_546782153d0ccd5501f5c4ddedb71ba1']