Returning numpy array in c extension causes Segmentation fault: 11

Question

I'm trying to write a c extension for python to speed up some number crunching I'm doing in my project with out having to port the whole thing to C. Unfortunately when I try to return numpy arrays by using my extension function in python it causes segmentation fault 11. Here's a minimal example below.

#include "Python.h"
#include "numpy/arrayobject.h"
#include <math.h>

static PyObject *myFunc(PyObject *self, PyObject *args)
{
    PyArrayObject *out_array;
    int dims[1];
    dims[0] = 2;
    out_array = (PyArrayObject *) PyArray_FromDims(1,dims,NPY_DOUBLE);

    // return Py_BuildValue("i", 1); // if I swap this return value it works
    return PyArray_Return(out_array);
}

static PyMethodDef minExMethiods[] = {
    {"myFunc", myFunc, METH_VARARGS},
    {NULL, NULL}     /* Sentinel - marks the end of this structure */
};

static struct PyModuleDef minExModule = {
    PyModuleDef_HEAD_INIT,
    "minEx",   /* name of module */
    NULL, /* module documentation, may be NULL */
    -1,       /* size of per-interpreter state of the module,
                 or -1 if the module keeps state in global variables. */
    minExMethiods
};

PyMODINIT_FUNC PyInit_minEx(void)
{   
    return PyModule_Create(&minExModule);
}

Can anyone suggest what I might be doing wrong? I'm using conda with a python 3.6 environment on OS X 10.13.6

thanks

Peter Clark · Accepted Answer · 2020-05-13 17:45:47Z

well showing my inexperience here but hopefully useful to others. I needed to call. import_array() in the modules initialisation function to use numpy's c helping functions properly. I also then got errors that PyArray_FromDims was depreciated. the fixed code bellow.

#include "Python.h"
#include "numpy/arrayobject.h"
#include <math.h>

static PyObject *myFunc(PyObject *self, PyObject *args)
{
    PyArrayObject *out_array;
    npy_intp dims[1];
    dims[0] = 2;
    out_array = (PyArrayObject *) PyArray_SimpleNew(1,dims,PyArray_DOUBLE);
    return PyArray_Return(out_array);
}

static PyMethodDef minExMethiods[] = {
    {"myFunc", myFunc, METH_VARARGS},
    {NULL, NULL}     /* Sentinel - marks the end of this structure */
};

static struct PyModuleDef minExModule = {
    PyModuleDef_HEAD_INIT,
    "minEx",   /* name of module */
    NULL, /* module documentation, may be NULL */
    -1,       /* size of per-interpreter state of the module,
                 or -1 if the module keeps state in global variables. */
    minExMethiods
};

PyMODINIT_FUNC PyInit_minEx(void)
{   
    PyObject *module = PyModule_Create(&minExModule);
    import_array();
    return module;
}

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