How to build a Python C Extension so I can import it from a module

Question

I have a Python project with many sub-modules that I package up with distutils. I would like to build some Python extensions in C to live in some of these sub-modules but I don't understand how to get the Python extension to live in a submodule. What follows is the simplest example of what I'm looking for:

Here is my Python extension c_extension.c:

#include <Python.h>  static PyObject * get_answer(PyObject *self, PyObject *args) {     return Py_BuildValue("i", 42); }  static PyMethodDef Methods[] = {     {"get_answer",  get_answer, METH_VARARGS, "The meaning of life."},     {NULL, NULL, 0, NULL} };  PyMODINIT_FUNC initc_extension(void) {   (void) Py_InitModule("c_extension", Methods); } 

And here is a setup.py that works:

from distutils.core import setup from distutils.extension import Extension  setup(name='c_extension_demo',       ext_modules = [Extension('c_extension', sources = ['c_extension.c'])]) 

After installing in an virtualenv I can do this:

>>> import c_extension >>> c_extension.get_answer() 42 

But I would like to have c_extension live in a sub-module, say foo.bar. What do I need to change in this pipeline to be able to get the behavior in the Python shell to be like this:

>>> import foo.bar.c_extension >>> foo.bar.c_extension.get_answer() 42 

Answer 1

Just change

Extension('c_extension', ...) 

to

Extension('foo.bar.c_extension', ...) 

You will need __init__.py files in each of the foo and bar directories, as usual. To have these packaged with the module in your setup.py, you need to add

packages = ['foo', 'foo.bar'], 

to your setup() call, and you will need the directory structure

setup.py foo/     __init__.py     bar/         __init__.py 

in your source directory.