How to add a built-in module to a C-Python API after Py_Initialize? - python-c-api

Question

I have a module defined in my C code like so:
static struct PyModuleDef module_def = {
PyModuleDef_HEAD_INIT,
"the_module_name", /* m_name */
module_documentation, /* m_doc */
//....
};
and a function to initialize it:
PyMODINIT_FUNC init_the_module(void)
{
PyObject *mod, *submodule;
PyObject *sys_modules = PyThreadState_GET()->interp->modules;
mod = PyModule_Create(&module_def);
PyModule_AddObject(mod, "some_submodule", (submodule = init_the_submodule()));
PyDict_SetItemString(sys_modules, PyModule_GetName(submodule), submodule);
Py_INCREF(submodule);
// more submodules..
return mod;
}
The application that I am embedding python into is quite big and I can not change the workflow much. At this point Py_Initialize has already been called, so I can not call PyImport_ExtendInittabor PyImport_AppendInittab .
How can I create and add the module to the system modules?
Maybe I can manipulate the modules dictionary directly? Like so:
PyObject *modules, *the_module;
modules = PyImport_GetModuleDict();
PyDict_SetItemString(modules, "the_module_name", init_the_module());
the_module = PyDict_GetItemString(modules, "the_module_name"); //this is getting something back
std::cout << PyDict_Size(the_module) << std::endl; // this prints -1

Answer 1

The easiest way to handle this is to statically initialize your statically-linked modules by directly calling initspam() after the call to Py_Initialize() or PyMac_Initialize():
int main(int argc, char **argv)
{
/* Pass argv[0] to the Python interpreter */
Py_SetProgramName(argv[0]);
/* Initialize the Python interpreter. Required. */
Py_Initialize();
/* Add a static module */
initspam();
An example may be found in the file Demo/embed/demo.c in the Python source distribution.