>>> data = [ ('Pre_session_username','Administrator'), ('Pre_session_password','univention'), ('Pre_session_language','de') ]
>>> x = urllib.urlopen('https://10.200.18.50/univention-directory-manager/index.php', urllib.urlencode(data))
>>> y = x.read()
>>> z = re.search('<input[^>]*?name="session_id"[^>]*?>', y).group(0)
>>> z
'<input type="hidden" name="session_id" value="0_5f4177f75df17e702b741237e87be5b8">'
>>> sessionid = re.search('''value=["'](._[a-f0-9]+)["']''', z).group(1)
>>> sessionid
'0_5f4177f75df17e702b741237e87be5b8'