I'm using the C API of numpy to write some functions for matrix calculation. Today I wanted to move some parts of my functions into a seperate .c file and use a header to declare them. Now I have a strange problem that has to do with numpy's import_array function. I've tried to simplify the problem as much as possible. At first there is the working program:

mytest.c

#include "mytest.h"

PyObject* my_sub_function() {
    npy_intp dims[2] = {2, 2};
    double data[] = {0.1, 0.2, 0.3, 0.4};

    PyArrayObject* matrix = (PyArrayObject*)PyArray_SimpleNew(2, dims, NPY_FLOAT64);
    memcpy(PyArray_DATA(matrix), data, sizeof(double) * dims[0] * dims[1]);

    return (PyObject*)matrix;
}

static PyObject* my_test_function(PyObject* self, PyObject* args) {
    return my_sub_function();
}

static PyMethodDef methods[] = {
    {"my_test_function", my_test_function, METH_VARARGS, ""},
    {0, 0, 0, 0}
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT, "mytest", 0, -1, methods
};

PyMODINIT_FUNC PyInit_mytest() {
    import_array();
    return PyModule_Create(&module);
}

mytest.h

#ifndef mytest_h
#define mytest_h

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

PyObject* my_sub_function();

#endif

Makefile

all: mytest.o sub.o
    gcc -shared -Wl,-soname,mytest.so -o mytest.so mytest.o

mytest.o: sub.o
    gcc -fPIC -c mytest.c `pkg-config --cflags python3`

clean:
    rm -rf *.so
    rm -rf *.o

Everything works as expected. I can call make and then load the module and call the function:

test.py

import mytest
print(mytest.my_test_function())

If I would remove import_array from the init function there would be a segfault, which is the behaviour that has

python c gcc numpy
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