请问Python利用telnetlib登录被ACL拒绝该如何处理异常？

 try:

    self.tn = telnetlib.Telnet(host_ip,port=23,timeout=2)

 except:

    logging.warning("failed to connect to host:%s" %host_ip)

    return False

 self.tn.read_until(b'Username:', timeout=3)

 self.tn.write(user_name.encode('ascii') + b'\n')

 self.tn.read_until(b'Password:', timeout=3)

 self.tn.write(pass_word.encode('ascii') + b'\n')