TypeError in HMAC module. topic

Hi,
I am trying to create a hashed message for authentication for a REST API
call. I have got the key from a keyring as :-

key = keyring.get_password('AWS_keyring','username')

& calculating the signature as :-
signature = hmac(key, message.encode('UTF-8'),
hashlib.sha1).digest().encode('base64')[:-1]

But, while running the script I get the following errors :-

File "/usr/lib64/python2.6/hmac.py", line 133, in new
return HMAC(key, msg, digestmod)
File "/usr/lib64/python2.6/hmac.py", line 72, in __init__
* self.outer.update(key.translate(trans_5C))*
*TypeError: character mapping must return integer, None or unicode*

My python version is :-

# python -V
Python 2.6.9

Can someone please help me as to how I can resolve this issue. Thanks in
advance.

--
*Thanks and Regards*
*Prabir Sarkar*