[Python-Dev] Feature request: better support for "wrapper" objects

[Jack Jansen]

Recently, "Thomas Heller" <thomas.heller@ion-tof.com> said:
> Here's an outline which could work in 2.2:

This sounds very good! There's only one thing you'll have to explain
to me: how would this work from C? My types are all in C, not in
Python, so I'd need to do the magic in C. Where do I find examples of
using metatypes from C?

I could then put all this wrapper stuff in a file WrapperObject.c and
it would be reusable by any object that wanted this functionality.

> Create a subtype of type, having a tp_convert slot:
> 
> typedef int (*convert_func)(PyTypeObject *, void **);
> 
> typedef struct {
>     PyTypeObject type;
>     convert_func tp_convert;
> } WrapperTypeType;
> 
> and use it as metaclass (metatype?) for your WindowObj:
> 
> class WindowObj(...):
>     __metaclass__ = WrapperTypeType
> 
> Write a function to return a conversion function:
> 
> convert_func *get_converter(PyTypeObject *type)
> {
>     if (WrapperTypeType_Check(type))
>         return ((WrapperTypeType *)type)->tp_convert;
>     /* code to check additional types and return their converters */
>     ....
> }
> 
> and then
> 
> if (!PyArg_ParseTuple(args, "O&", get_converter(WinObj_Type), &Window))
> 
> How does this sound?
> 
> Thomas
> 
> 
--
- Jack Jansen        <Jack.Jansen@oratrix.com>        http://www.cwi.nl/~jack -
- If I can't dance I don't want to be part of your revolution -- Emma Goldman -