member array in c passed to python?

[Alex Martelli]

William Hanlon wrote:

> Hi,
> 
> I would like to use the Python C API to use python to access functions
> originally written in C. The objects that I would like to pass to python
> have multi-dimensional arrays.
> 
> How do I include arrays as object member? And how is it declared in the
> PyMemberDef array?

You can, if you wish, construct and expose a new "array" type from
within your extension -- or reuse those already constructed for you
by the Numeric package.


> If you can not use C arrays, I thought perhaps then I should use Python
> tuples or lists, but I don't see how to fill the tuple from the
> multi-dimensional arrays. Does anyone have an example of this?

You have to know the number of dimensions and proceed accordingly,
For example, for a 2-dimensional array of integers you could do 
something like:

PyObject*
array_to_list_2d(int **array, int N, int M)
{
    PyObject * temp;
    PyObject * result = PyList_New(N);
    for(i = 0; i < N; i++) {
        PyList_SET_ITEM(result, i, temp = PyList_NEW(M));
        for(j = 0; j < M; j++)
            PyList_SET_ITEM(temp, j, PyInt_FromLong(array[i][j]));
    }
    return result;
}

However, this does need a lot of data copying and object allocation,
which you might obviate if you were to use your own data type (or
reuse Numeric's) to wrap your existing arrays.


Alex