[Python-Dev] Simpler reformulation of C inheritance Q.

Christian Tismer tismer@tismer.com
Tue, 06 Aug 2002 12:02:14 +0200

Guido van Rossum wrote:

>>From Christian's post I can't tell if he wants his types to be dynamic
> or static (i.e. if he's creating an arbitrary number of them at
> run-time or only a fixed number that's known at compile-time).

I'm not absolutely sure what I meant. Actually, I wanted to
cache existing methods, which are known at compile-time.
At run-time, they would be replaced for derived types.
But a run-time solution might make sense, to generate
very fast class variables, maybe.

> Here's a hack.
> For static extensions, you could extend one of the extension structs,
> e.g. PyMappingMethods (which is the smallest and also least likely to
> grow new methods), with additional fields.  Then you'd have to know
> whether you can access those extra fields; I suggest checking for the
> metatype.  A few casts and you're done.
> For dynamic extensions, you might be able to do the same: after
> type_new() has given you an object, allocate memory for an extended
> PyMappingMethods struct, copy the existing PyMappingMethods struct
> into it (if it exists), and replace the pointer.  Then in your
> deallocation function, make sure to free the pointer.
> Hope this helps in the short run.

Thanks a lot. Yes, it helps in the short run, but stays
a hack. I'm trying to find a way that allows meta-types
to support slots for its type instances without introducing
too much special-casing.
What I do not understand yet is who uses the variable type
part and in which way. I'd like to collaborate with it.

ciao - chris

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