[Numpy-discussion] Global Numpy vector with Swig

Bill Spotz wfspotz@sandia....
Fri Feb 16 14:10:12 CST 2007


Andrea,

It is my understanding that swig typemaps only apply to function  
arguments.  Since what you are talking about is a global variable, I  
don't believe typemaps will help you.  I would try

%{
#include "header-that-contains-vec.h"
npy_intp vec_dims[ ] = { (npy_intp) length_of_vec };
%}
%rename(vec) numpy_vec;
%ignore vec;
%include "header-that-contains-vec.h"
%inline %{
PyObject * numpy_vec = PyArray_SimpleNewFromData(1, vec_dims,  
NPY_DOUBLE, (void*)vec);
%}

I guess it would be nice if you could force a "Py_DECREF(numpy_vec);"  
before the module is destroyed, but I'll leave that as an exercise...

On Feb 16, 2007, at 10:59 AM, Andrea Tomadin wrote:

> Il giorno 15/feb/07, alle ore 22:26, Bill Spotz ha scritto:
>
>> It seems to me you would need to %ignore vec, so that it is not
>> wrapped as a raw pointer to a double, and then in your interface
>> file create a PyArrayObject whose data buffer points to vec (the
>> most efficient way to do this is with %inline).  Then use %rename
>> to rename whatever you called your PyArrayObject to "vec" (or not,
>> if you do not care about the name).  Finally,
>>
>>   foo.cvar.vec = numpy.zeros(10)
>>
>> is going to decrement (and probably delete) your original vec and
>> replace it with the new array of zeros (I think,
>
> Thank you Bill for your help, even if writing this code is not
> straightforward for me. Anyway, while I was reading the docs, I
> became aware of the varin, varout typemap options. I wonder if I can
> define a
> typemap(varin) double *
> declaration, and insert in it the same code that in "numpy.i"
> translates the PyArrayObject into a C array and vice versa.
> But I cannot find an example of typemp(varin) for Python, so I don't
> know what to use for the output, instead of $1. Where are the typemaps
> (varin) for Python?
> It seems strange that nobody wrote a public code for such a simple
> task, as I read that Swig supports Python since the 90s! I suspect I
> have just not looked in the right places?!
>
> Thank you again for help!
> Andrea

** Bill Spotz                                              **
** Sandia National Laboratories  Voice: (505)845-0170      **
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