Makefile

PRFX=$(HOME)/autobuild/build-Linux-pre-release-gtk3-python

CXXFLAGS=-I$(PRFX)/include/python3.6m/
LDFLAGS=-L$(PRFX)/lib -lpython3.6m -Wl,-rpath=$(PRFX)/lib

all: standalone-python-test

standalone-python-test: standalone-python-test.cc
	$(CXX) $^ $(CXXFLAGS) -o $@ $(LDFLAGS)

test:
	python3 -c "import myextension"

standalone-python-test.cc

#include "Python.h"

#include <iostream>

struct module_state {
    PyObject *error;
};

#define GETSTATE(m) ((struct module_state *)PyModule_GetState(m))

static PyObject *error_out(PyObject *m) {
    struct module_state *st = GETSTATE(m);
    PyErr_SetString(st->error, "something bad happened");
    return NULL;
}

static PyMethodDef myextension_methods[] = {
    {"error_out", (PyCFunction)error_out, METH_NOARGS, NULL}, {NULL, NULL}};

static int myextension_traverse(PyObject *m, visitproc visit, void *arg) {
    Py_VISIT(GETSTATE(m)->error);
    return 0;
}

static int myextension_clear(PyObject *m) {
    Py_CLEAR(GETSTATE(m)->error);
    return 0;
}

static struct PyModuleDef moduledef = {
    PyModuleDef_HEAD_INIT,       "myextension",       NULL,
    sizeof(struct module_state), myextension_methods, NULL,
    myextension_traverse,        myextension_clear,   NULL};

PyObject *PyInit_myextension(void) {
    PyObject *module = PyModule_Create(&moduledef);

    if (module == NULL) return NULL;
    struct module_state *st = GETSTATE(module);

    st->error = PyErr_NewException("myextension.Error", NULL, NULL);
    if (st->error == NULL) {
        Py_DECREF(module);
        return NULL;
    }
    if (PyErr_Occurred()) PyErr_PrintEx(0);

    return module;
}

void initcoot_python_gobject() {
    

    if (true) {
        PyObject *o = PyInit_myextension();

        // Insert this into sys.modules directly
        PyObject *sys = PyImport_ImportModule("sys");
        PyObject *modules = PyObject_GetAttrString(sys, "modules");
        PyDict_SetItemString(modules, "myextension", o);
        Py_DECREF(modules);
        Py_DECREF(sys);

        PyObject *impmod = PyImport_ImportModule("myextension");
        if (PyErr_Occurred()) PyErr_PrintEx(0);
        std::cout << "impmod: " << impmod << std::endl;
    }
}

int main(int argc, char **argv) {
    int status = 0;

    wchar_t **_argv = static_cast<wchar_t **>(PyMem_Malloc(sizeof(wchar_t *) * argc));
    for (int i = 0; i < argc; i++) {
        wchar_t *arg = Py_DecodeLocale(argv[i], NULL);
        _argv[i] = arg;
    }

    Py_InitializeEx(0);
    initcoot_python_gobject();
    Py_Main(argc, _argv);
    return status;
}