Makefile

CC = gcc
CFLAGS = -g -Wall -fPIC -std=gnu99 -O3 -march=native

all: libtest.so

libtest.so: test.o
	$(CC) -shared -Wl,-soname,libtest.so -o libtest.so $<

%.o: %.c
	$(CC) -c $(CFLAGS) $<

clean:
	rm -vf libtest.so test.o

test.c

#include "test.h"

void callback_test(double* x, int n, callback_t callback) {
	for(int i = 1; i <= 5; i++) {

		for(int j = 0; j < n; j++) {
			x[j] = x[j] / i;
		}

		callback(x, n);
	}
}

test.h

typedef void (*callback_t)(
	double *x,
	int n
);

void callback_test(double* x, int n, callback_t callback);

test.py

#!/usr/bin/env python

import numpy as np
import numpy.ctypeslib as npct
import ctypes
import os.path

array_1d_double = npct.ndpointer(dtype=np.double, ndim=1, flags='CONTIGUOUS')

callback_func = ctypes.CFUNCTYPE(
    None,            # return
    ctypes.POINTER(ctypes.c_double), # x
    ctypes.c_int     # n
)

libtest = npct.load_library('libtest', os.path.dirname(__file__))
libtest.callback_test.restype = None
libtest.callback_test.argtypes = [array_1d_double, ctypes.c_int, callback_func]


@callback_func
def callback(x, n):
    print("x: {0}, n: {1}".format(x[:n], n))


if __name__ == '__main__':
    x = np.array([20, 13, 8, 100, 1, 3], dtype=np.double)
    libtest.callback_test(x, x.shape[0], callback)