unicode and data strings

[Laszlo Zsolt Nagy]

Hello

I have a program where I would like to calculate a checksum. Looks like 
this:

n = self.__calc_n(seed1,seed2,pwd)

This is required for an OTP (One Time Password) algorithm. My code was 
working before without problems.
Now I installed Python 2.3.4 and wxPython 2.5.3 (with unicode support). 
I'm getting this exception:

exceptions.UnicodeDecodeError:'ascii' codec can't decode byte 0x91 in 
position 0: ordinal not in range(128)

The I tried this:

 >>>'\x91'.decode('utf8')
UnicodeDecodeError: 'utf8' codec can't decode byte 0x91 in position 0: 
unexpected code byte

Here is the question: I would like to use simple binary data strings 
(like an array of bytes).
I do not care about encodings. How do I do that?

Thanks,

   Laci 2.0