Subclassing String in C

[Robin Becker]

A client program wants to pass my code truetype font files which have
already been loaded in memory. Our existing Python/c code reads ttf
files into memory as strings. I can easily do the same providing the
client knows the data length.

I would like to avoid the memory overhead of n+1 bytes which that would
involve by making a kind of readonly string that refers directly to the
client memory.

I can think of two possible approaches 1) implement a buffer compatible
type from scratch 2) co-opt PyString_Type to subclass String and
implement a special version of PyString_FromStringAndSize that doesn't
copy and ensure that deallocation is handled properly.

Any body already invented this kind of wheel? Are there obvious pitfalls
(other than dangling reference issues etc)? 
-- 
Robin Becker