[Pyrex] How do I return a PyObject * from python functions?

[Robert Bradshaw]

Try using the object type. (This is simply a PyObject* that is  
refcounted). E.g.

cdef extern from "numpy/arrayobject.h":
     cdef object PyArray_SimpleNewFromData(int nd, int * dims, int  
typenum,char * data)

(This assumes that PyArray_SimpleNewFromData gives you a new  
reference, check the numpy documentation for that.)

On Sep 21, 2007, at 3:30 PM, Roy Dragseth wrote:

> Hi, I might be missing something obvious here, but I'm really stuck.
>
> I want to wrap a c-function that returns some data in a c-type  
> array by
> creating a numpy array. So far so good, pyrex is really much easier  
> than
> anything else I've come across.  But, when I use the standard  
> interface for
> creating a numpy array from already allocated data I find that the  
> function
> PyArray_SimpleNewFromData returns a PyObject pointer which points  
> to the
> numpy array.  How on earth do I get that propagated out as a numpy  
> array
> return value from the python function?
>
> Below is an example code illustrating the problem.  When I compile  
> it with
> pyrexc it says:
> $ pyrexc pyrextest.pyx
> /home/royd/python/ga/pyrextest.pyx:34:11: Cannot convert 'PyObject  
> (*)' to
> Python object
>
> Which of course makes sense as that is what I'm trying to do, but  
> how do I
> convert a PyObject * to python object that can be returned?
>
> Any help is greatly appreciated.
>
> Regards,
> r.
>
>
> Here is pyrextest.pyx (it is stripped down to illustrate my problem):
> # standard defs
> ctypedef int size_t
>
> cdef extern from "stdlib.h":
>     cdef void *malloc(size_t)
>     cdef void free(void *)
>
> cdef extern from "object.h":
>     ctypedef struct PyObject:
>         pass
>
> cdef extern from "numpy/arrayobject.h":
>     cdef int NPY_CARRAY "NPY_CARRAY"
>     cdef void import_array()
>
>     cdef PyObject * PyArray_SimpleNewFromData(int nd, int * dims,
>         int typenum,char * data)
>
> import_array()
>
> def create_array():
>     cdef int dims[2]
>     cdef void *ptr
>     cdef int ndim
>     cdef PyObject* arr
>
>     #Just create some space.
>     dims[0] = 5
>     dims[1] = 20
>     ptr = malloc(sizeof(1.0)*100)
>     #create a new numpy array that wraps ptr.
>     arr = PyArray_SimpleNewFromData(ndim,dims,NPY_CARRAY,
>                             <char *> ptr)
>     return arr
>
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