Implementing new encodings in python

[Pascal Bach]

Hello,

I'm trying to implement a new character encoding defined in the GSM
standard. The problem is that the encoding uses an extension table
with an escaping character so I can not us a simple charmap. I think I
have to use an IncrementalEncoder/Decoder but the problem is I don't
know how to do it.

If somebody can tell me how I have to do it, or even point me to an
example?

Thank you for you help

Regards,
Pascal