Does anybody here have experience about offering the array interface
from a SWIG-wrapped C struct?
I have tried the following, borrowing code from numpy's arrayobject.c:
%extend real_vec_t {
PyObject *__array_struct__() {
/* From numpy/arrayobject.c/array_struct_get */
PyArrayInterface *inter;
inter = (PyArrayInterface *)_pya_malloc(sizeof(PyArrayInterface));
inter->two = 2;
inter->nd = 1;
inter->typekind = 'f';
inter->itemsize = sizeof(float);
inter->flags = (NPY_CONTIGUOUS | NPY_OWNDATA | NPY_ALIGNED |
NPY_NOTSWAPPED);
inter->shape = (intp *)_pya_malloc(2*sizeof(intp));
inter->strides = inter->shape + 1;
*(inter->shape) = self->n;
*(inter->strides) = 1;
inter->data = (void *)(self->d);
inter->descr = 0;
return PyCObject_FromVoidPtr(inter,0);
}
%}
When passing such a SWIG real_vec_t object to numpy.array, numpy gets
a PyArrayInterface that fails to check correctly as a Python C
object. Three comments:
- The original numpy/arrayobject.c code actually gets its return
value from PyCObject_FromVoidPtrAndDesc(inter,self,...); but in this
context self does not point to a PyObject, but rather to the C
struct, so I don't think I can use that form.
- The code above does not deal with properly destructing the
PyArrayInterface, setting refcounts, etc. But I was going to worry
about those later.
- My problem is probably with SWIG rather than numpy... but I thought
the people in this forum (rather than those at the SWIG forum) would
be most likely to have encountered a situation similar to these.
Thanks a lot for any help, or just for reading this post.
Michele
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