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Vebjorn Ljosa
Vebjorn Ljosa

Reputation: 18008

How to create a numpy record array from C

On the Python side, I can create new numpy record arrays as follows:

numpy.zeros((3,), dtype=[('a', 'i4'), ('b', 'U5')])

How do I do the same from a C program? I suppose I have to call PyArray_SimpleNewFromDescr(nd, dims, descr), but how do I construct a PyArray_Descr that is appropriate for passing as the third argument to PyArray_SimpleNewFromDescr?

Upvotes: 9

Views: 4840

Answers (2)

Vebjorn Ljosa
Vebjorn Ljosa

Reputation: 18008

Use PyArray_DescrConverter. Here's an example:

#include <Python.h>
#include <stdio.h>
#include <numpy/arrayobject.h>

int main(int argc, char *argv[])
{
     int dims[] = { 2, 3 };
     PyObject *op, *array;
     PyArray_Descr *descr;

     Py_Initialize();
     import_array();
     op = Py_BuildValue("[(s, s), (s, s)]", "a", "i4", "b", "U5");
     PyArray_DescrConverter(op, &descr);
     Py_DECREF(op);
     array = PyArray_SimpleNewFromDescr(2, dims, descr);
     PyObject_Print(array, stdout, 0);
     printf("\n");
     Py_DECREF(array);
     return 0;
}

Thanks to Adam Rosenfield for pointing to Section 13.3.10 of the Guide to NumPy.

Upvotes: 11

Adam Rosenfield
Adam Rosenfield

Reputation: 400274

See the Guide to NumPy, section 13.3.10. There's lots of different ways to make a descriptor, although it's not nearly as easy as writing [('a', 'i4'), ('b', 'U5')].

Upvotes: 6

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