[Pyrex] metaclasses for c extension types

[Simon Burton]

On Mon, 08 Aug 2005 15:25:07 +1200
Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

> 
> Simon Burton wrote:
> 
> > I see the __metaclass__ attribute is not supported for cdef classes.
> 
> > I'm wondering if this is even theoretically possible (eg. by hacking the c code).
> 
> This would be difficult, since extension types are created
> a completely different way from Python classes. Instead of
> calling a metaclass, the type object is statically allocated
> and initialised by calling PyType_Ready.
> 
> What are you trying to accomplish with a metaclass? There
> may be another way of getting the same effect.

I'm building a type system similar to ctypes: classes to represent c-level objects (int, void* etc).
These classes need (among other things) a __getattr__ so i can write CInt.pointer to mean "int*".

It seems that today i'm getting some mileage out of inheriting from the extension types with a metaclass:

class Meta(type):
  def __getattr__( cls, name ):
    if name == "pointer":
      tp = type( "CPointer"+cls.__name__, (CPointer,), {} )
      tp.target = cls
      return tp

CInt = Meta( "CInt", (CInt,), {} )

This only works at the python level, of course.

cheers,

Simon.

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Simon Burton, B.Sc.
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