10.7.2 : The C++ module file

Now, let's write the sgemmpython.cpp file :



First, we have to activate the numpy we disabled in the previous files. Otherwise, you will get a segmentation fault out of knowhere.

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#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#ifndef DISABLE_COOL_ARRAY
#define PY_ARRAY_UNIQUE_SYMBOL core_ARRAY_API
#endif


Then, we include all the previous wrapper and the python stuff, of course.

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#include <iostream>

#include <Python.h>
#include "structmember.h"
#include <numpy/arrayobject.h>

#include "sgemmWrapper.h"


It is always good to have a documentation of your function. The folowing will appear when you call a function with '?' or shift-tab in jupyter-notebook :

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std::string sgemmWrapper_docstring = "Compute a SGEMM product with aligned matrices of float32 with a pitch\n\
Parameters :\n\
	matRes : matrix of the results (float32 aligned)\n\
	matX :   matrix of value (float32 aligned)\n\
	matY :   matrix of value (float32 aligned)";


We define the callable method of our wrapper :

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static PyMethodDef _sgemm_methods[] = {
	{"sgemm", (PyCFunction)sgemmWrapper, METH_VARARGS, sgemmWrapper_docstring.c_str()},
	{NULL, NULL}
};


Notice that you can expose the functions you want, not all the functions you developed.


Now, we have to define the python module itself :

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static PyModuleDef _sgemm_module = {
	PyModuleDef_HEAD_INIT,
	"sgemmpython",
	"",
	-1,
	_sgemm_methods,
	NULL,
	NULL,
	NULL,
	NULL
};


Now we define the function which will be called on the import of our module.

Notice you must call this function PyInit_NameOfYouModule where NameOfYouModule is the name of THIS file.


We create the module, which is a PyObject.

Do not forget to call import_array otherwise you will get a warning on the best cases and a segmentation fault on your module import. 


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///Create the python module sgemm
/**	@return python module sgemm
*/
PyMODINIT_FUNC PyInit_sgemmpython(void){
	PyObject *m;
	import_array();
	
	m = PyModule_Create(&_sgemm_module);
	if(m == NULL){
		return NULL;
	}
	return m;
}


The full sgemmpython.cpp file :

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/***************************************
	Auteur : Pierre Aubert
	Mail : pierre.aubert@lapp.in2p3.fr
	Licence : CeCILL-C
****************************************/

#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION
#ifndef DISABLE_COOL_ARRAY
#define PY_ARRAY_UNIQUE_SYMBOL core_ARRAY_API
#endif

#include <iostream>

#include <Python.h>
#include "structmember.h"
#include <numpy/arrayobject.h>

#include "sgemmWrapper.h"

std::string sgemmWrapper_docstring = "Compute a SGEMM product with aligned matrices of float32 with a pitch\n\
Parameters :\n\
	matRes : matrix of the results (float32 aligned)\n\
	matX :   matrix of value (float32 aligned)\n\
	matY :   matrix of value (float32 aligned)";

static PyMethodDef _sgemm_methods[] = {
	{"sgemm", (PyCFunction)sgemmWrapper, METH_VARARGS, sgemmWrapper_docstring.c_str()},
	{NULL, NULL}
};

static PyModuleDef _sgemm_module = {
	PyModuleDef_HEAD_INIT,
	"sgemmpython",
	"",
	-1,
	_sgemm_methods,
	NULL,
	NULL,
	NULL,
	NULL
};

///Create the python module sgemm
/**	@return python module sgemm
*/
PyMODINIT_FUNC PyInit_sgemmpython(void){
	PyObject *m;
	import_array();
	
	m = PyModule_Create(&_sgemm_module);
	if(m == NULL){
		return NULL;
	}
	return m;
}


You can download it here.