Makefile

CC = gcc
CFLAGS = -g -Wall -fPIC -lm -std=gnu99 -O3 -march=native -DCONJUGRAD_FLOAT=64

all: libmyfunc.so

m.PHONY : clean

libmyfunc.so: myfunc.o
	gcc -shared -Wl,-soname,$@ -o $@ $^

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

clean:
	rm -vf libmyfunc.so *.o

myfunc.c

#include "myfunc.h"

double myfunc(mystruct_t* data) {

	double result = 0.;

	for(int i = 0; i < data->n; i++) {
		result += data->x[i];
	}

	return result;
}

myfunc.h

typedef struct mystruct_t {
	int n;
	double *x;
} mystruct_t;

double myfunc(mystruct_t* data);

myfunc.py

#!/usr/bin/env python
import numpy as np
import numpy.ctypeslib as npct
import ctypes
import os

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


class MyStruct(ctypes.Structure):
    _fields_ = [
        ('n', ctypes.c_int16),
        ('x', array_1d_double)
    ]

libmyfunc = npct.load_library('libmyfunc', os.path.dirname(__file__))
libmyfunc.myfunc.restype = ctypes.c_double
libmyfunc.myfunc.argtypes = [
    ctypes.POINTER(MyStruct)
]

x = np.array([1.0, 2.0, 3.0, 4.0])

mystruct = MyStruct()
mystruct.n = len(x)
mystruct.x = x

res = libmyfunc.myfunc(mystruct)