python base64 decode incorrect padding错误解决方法

python的base64.decodestring方法做base64解码时报错：

代码如下：

Traceback (most recent call last):

  File "/export/www/outofmemory.cn/controllers/user.py", line 136, in decryptPassword

    encryptPwd = base64.b64decode(encryptPwd)

  File "/usr/lib/python2.7/base64.py", line 76, in b64decode

    raise TypeError(msg)

TypeError: Incorrect padding

代码如下：

        def decode_base64(data):

            """Decode base64, padding being optional.

            :param data: Base64 data as an ASCII byte string

            :returns: The decoded byte string.


            """

            missing_padding = 4 - len(data) % 4

            if missing_padding:

                data += b'='* missing_padding

            return base64.decodestring(data)