[Python-Dev] marshal (was:Buffer interface in abstract.c? )

[M.-A. Lemburg]

Jack Jansen wrote:
> 
> Recently, Greg Stein <gstein@lyra.org> said:
> > I would suggest backing out the marshalling of buffer-interface objects
> > and adding a mechanism for arbitrary type objects to marshal themselves.
> > Without the second part, arrays and Unicode objects aren't marshallable
> > at all (seems bad).
> 
> This sounds like the right approach. It would require 2 slots in the
> tp_ structure and a little extra glue for the typecodes (currently
> marshall knows all the 1-letter typecodes for all objecttypes it can
> handle, but types marshalling their own objects would require a
> centralized registry of object types. For the time being it would
> probably suffice to have the mapping of type<->letter be hardcoded in
> marshal.h, but eventually you probably want a more extensible scheme,
> where Joe R. Extension-Writer could add a marshaller to his objects
> and know it won't collide with someone else's.

This registry should ideally be reachable via C APIs. Then a module
writer could call these APIs in the init function of his module and
he'd be set. Since marshal won't be able to handle imports on the
fly (like pickle et al.), these modules will have to be imported
before unmarshalling.

Aside: wouldn't it make sense to move from marshal to pickle and
depreciate marshal altogether ? cPickle is quite fast and much more
flexible than marshal, plus it already provides mechanisms for
registering new types.

-- 
Marc-Andre Lemburg
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