[Python-Dev] Extending types in C - help needed

[Thomas Heller]

From: "Jack Jansen" <Jack.Jansen@oratrix.nl>
> In the discussion on my request for an ("O@", typeobject, 
> void **) format for PyArg_Parse and Py_BuildValue MAL suggested 
(as MAL already explained, that we suggested by me)
> that I could get the same functionality by creating a type 
> WrapperTypeObject, which would be a subtype of TypeObject with 
> extra fields pointing to the _New() and _Convert() routines to 
> convert Python objects from/to C pointers. This would be good 
> enough for me, because then types wanting to participate in the 
> wrapper protocol would subtype WrapperTypeObject in stead of 
> TypeObject, and two global routines could return the _New and 
> _Convert routines given the type object, and we wouldn't need 
> yet another PyArg_Parse format specifier.
> 
> However, after digging high and low I haven't been able to 
> deduce how I would then use this WrapperType in C as the type 
> for my extension module objects. Are there any examples? If not, 
> could someone who understands the new inheritance scheme give me 
> some clues as to how to do this?

Currently (after quite some time) I have the impression that you
cannot create a subtype of PyType_Type in C because PyType_Type
ends in a variable sized array, at least not in this way:

struct {
    PyTypeObject type;
    ...additional fields...
} WrapperType_Type;

Can someone confirm this?

(I have to find out what to do with the tp_members slot, which seems to be
correspond to the Python level __slots__ class variable)

Thomas