migrating from python 2 to python 3 - embedding issues

Question

i am migrating an application that embeds python, from version 2.7 to version 3.3. The application makes functions available to script, by calling Py_InitModule() with the appropriate data. Just to annoy poor guys like me, the api was dropped in python 3 and replaced by PyModule_Create, which takes a fairly complex structure.

When i use the python2 api, everything works fine, when i use the new v3 one, the api loads fine (returns a valid pointer), but using the exposed functions in a script will yield an error:

//ImportError: No module named 'emb'

Where emb is my module name. Very annoying! I have included the two version, maybe someone can help. I followed the porting guide here:

http://docs.python.org/3/howto/cporting.html

which does exactly the same thing as me. Why the api was changed is beyond me.

static int numargs=0;
static PyObject*
emb_numargs(PyObject *self, PyObject *args) //what this function does is not important
{
 if(!PyArg_ParseTuple(args, ":numargs"))
 return NULL;
 return Py_BuildValue("i", numargs);
}
static PyMethodDef EmbMethods[] = {
 {"numargs", emb_numargs, METH_VARARGS,
 "Return the number of arguments received by the process."},
 {NULL, NULL, 0, NULL}
};
#ifdef PYTHON2
 //works perfect with Pytho 27
 Py_InitModule("emb", EmbMethods);
 PyRun_SimpleString(
 "import emb\n"
 "print(emb.numargs())\n"
 ); 
#else
static struct PyModuleDef mm2 = {
 PyModuleDef_HEAD_INIT,
 "emb",
 NULL,
 sizeof(struct module_state),
 EmbMethods,
 NULL,
 0,
 0,
 NULL
};
 //does not work with python 33:
 //ImportError: No module named 'emb'
 PyObject* module = PyModule_Create(&mm2);
 PyRun_SimpleString(
 "import emb\n"
 "print(emb.numargs())\n"
 );
#endif

Answer 1

Based off this issue it seems they have changed the way to import modules has also changed.

Here is what should hopefully work for you:

// this replaces what is currently under your comments
static PyObject*
PyInit_emb(void)
{
 return PyModule_Create(&mm2);
}
numargs = argc;
PyImport_AppendInittab("emb", &PyInit_emb);

• bernd feinman: perfect, thanks! Though i am really starting to dislike the python c api... For others: Note that PyImport_AppendInittab should be called before PyInitilaize() or the import will not be found.