create a python module with C and Python code

Question

I have a small python module I have created with the Python C API which I call mycore.

I have also created some utility scripts in Python which are related.

How can I put both in the same module namespace? I know I can call Python code from my C code but surely there is an easier way to do that.

Thanks

• Aida Paul: Did you play around with boost python?
• don_q: I'm quite happy with the C API
• Jiminion: I have the same question.

Answer 1

The obvious way is by making mycore a package. Create a mycore/__init__.py that imports both the C part, typically named something like _mycore, and the Python part:

from _mycore import *
from _mycorepy import *

In the same directory you'd have a _mycore.so and _mycorepy.py.

Another way to mix Python and C code is by invoking PyRun_String on the embedded Python. This might be what you mean by I know I can call Python code from my C code..., but just in case, here is a simple example with the potentially tricky refcounting details:

PyObject *get_factory()
{
 PyObject *g, *runret, *factory;
 // prepare a dictionary for the module to run in
 g = Py_BuildValue("{s:O}", "__builtins__", PyEval_GetBuiltins());
 if (!g)
 return NULL;
 // run Python code in the dictionary -- the code may import modules, etc.
 runret = PyRun_String("\
def factory():\n\
 return 42\n", Py_file_input, g, NULL);
 Py_XDECREF(runret);
 if (!runret) {
 Py_DECREF(g);
 return NULL;
 }
 Py_DECREF(runret);
 // pick the stuff you care about from the dictionary and return it
 factory = PyDict_GetItemString(g, "factory");
 Py_INCREF(factory);
 Py_DECREF(g);
 return factory;
}

• don_q: Is this the best resource for learning about packages? guide.python-distribute.org/creation.html Also, why the underscore before the mycore* ?
• user4815162342: @user3275885 The link appears to be about distributing on PyPI and others. The answer refers to Python packages, which are simply modules spread into several files, defined by a directory with __init__.py. The underscore in _mycore signifies that mycore._mycore is an implementation detail of the mycore package, and not something the user of the package should be importing themselves.
• don_q: the PyRun_String() will surely work, but I was hoping to avoid any extra "glue" . Thank you @user4815162342

Answer 2

OK, this worked for me. My circumstances may be different. My C module was built internally and provided to my embedded Python with a call to PyImport_AppendInittab().

But I still had some accompanying Python code that I wanted associated with the same namespace.

So I got it working by naming my C code _mygadget and the Python file mygadget.py. For the first line of mygadget.py I wrote:

from _mygadget import *

This seems to work. I don't know what would happen if I had a Python method and C call with the same name. I am avoiding that at present.