[Pyrex] Calling Pyrex from another Python module

[Nicholas Riley]

On Thu, Jan 04, 2007 at 07:55:44AM +0100, konrad.hinsen at laposte.net wrote:
> Much of my code does C-function calls between two extension modules  
> written in C. Each module makes its callable C functions visible  
> through a CObject. The calling module obtains this CObject through  
> the standard import mechanism. At some time I wrote a section about  
> this mechanism for the "Python extending and embedding" manual; I  
> suppose it's still in there.

Yes, thanks, I found that very useful. I was hoping for a
Pyrex-specific method but there doesn't seem to be one (or, really,
any need for one).

> I have never used this approach with Pyrex, but I don't see why it  
> shouldn't be possible, given that Pyrex can create pretty much any C  
> code.

The only issue is that Pyrex appears to be unable to create static
arrays easily, that I could figure out, so I just put the object
directly into the module namespace instead.

I declared my function as follows:

cdef public void MROWatcher_OnChangeRespawn(type_, name,
                                            void *write_jmp, void *codestart):

then created a PyCObject:

cdef extern from "cobject.h":
    object PyCObject_FromVoidPtr(void *cobj, void (*destruct)(void *))

_MROWatcher_OnChangeRespawn = \
    PyCObject_FromVoidPtr(<void *>MROWatcher_OnChangeRespawn, NULL)

and called it from C, where I made use of the prototype exported by
Pyrex:

#include "pyUFO.h"
[...]

  static typeof(MROWatcher_OnChangeRespawn) *OnChangeRespawn = NULL;
  if (OnChangeRespawn == NULL) {
     PyObject *c_object =
       PyObject_GetAttrString(UFOModule, "_MROWatcher_OnChangeRespawn");
     assert(c_object != NULL);
     OnChangeRespawn = (typeof(MROWatcher_OnChangeRespawn) *)
                          PyCObject_AsVoidPtr(c_object);
     Py_DECREF(c_object);
  }
  OnChangeRespawn(type, name, rs->write_jmp, rs->self->codestart);

The latter could be encapsulated in a macro pretty easily, but right
now this is the only function I need to call from C.

-- 
Nicholas Riley <njriley at uiuc.edu> | <http://www.uiuc.edu/ph/www/njriley>