python: ImportError: dynamic module does not define module export function - python-3.x

Question

im trying to install my function written in c (with python3 setup.py install) but python raise ImportError: dynamic module does not define module export function (PyInit_costFunction)
error!
costFunction.c:
static PyObject *costFunction(PyObject *self, PyObject *args)
{
return Py_BuildValue("d", 0); // or anything!
}
static PyMethodDef costFunction_methods[] = {
{"costFunction", (PyCFunction)costFunction, METH_VARARGS, "cost function"},
{NULL, NULL, 0, NULL}
};
static struct PyModuleDef costFunctionmodule = {
PyModuleDef_HEAD_INIT,"costFunction", NULL, -1, costFunction_methods
};
PyMODINIT_FUNC PyInit_costFunction(void)
{
return PyModule_Create(&costFunctionmodule);
}
setup.py:
from distutils.core import setup, Extension
setup(name='costFunction', version='1.0', \
ext_modules=[Extension('costFunction', ['costFunction.c'],include_dirs=['include'])])
external library: tinyexpr
i'm using linux mint 18 with python 3.5.2
EDIT:
python3-dev version is 3.5.1-3

Answer 1

finally i used an dirty trick!
compiled c code(without python.h and any python datatype in C) with:
gcc -fPIC -Wall -O3 costFunction.c -o costFunction.so -shared -fopenmp
and used python ctypes module to load and use it:
dll = ctypes.CDLL("./costFunction.so")
costFunction = dll.cost_function
costFunction.restype = ctypes.c_double
costFunction.argtypes = [ctypes.POINTER(ctypes.c_double), ctypes.c_int]