Python Extending

py.cpp

// py.cpp : Defines the entry point for the console application.
//

#include <Python.h>
#include <math.h>

/* This method will be exported as part of the test_embed package for use in imported
   python modules:
      import test_embed
      test_embed.emb_pow(x,y)
*/
static PyObject* emb_pow(PyObject *self, PyObject *args) {
    int x, y;
    if (PyArg_ParseTuple(args, "ii", &x, &y)) {
        //this is really just an awful thing to do as an example
        int result = pow((double)x,(double)y);
        return Py_BuildValue("i", result);
    }
    return NULL;
}

/* Define which methods are members of the test_embed module for exporting */
static PyMethodDef EmbMethods[] = {
    {"emb_pow", emb_pow, METH_VARARGS,
     "return pow(x,y)"},
    {NULL, NULL, 0, NULL}
};


int main(int argc, char* argv[])
{
    //set python home directory to somewhere easier to redistribute i.e. Python27/ relative to exe directory
    /*
    char pySearchPath[] = "Python27";
    Py_SetPythonHome(pySearchPath);*/

    //See: http://docs.python.org/extending/embedding.html#pure-embedding
    PyObject *pName, *pModule, *pDict, *pFunc;
    PyObject *pArgs, *pValue;
    int i;

    if (argc < 3) {
        fprintf(stderr,"Usage: call pythonfile funcname [args]\n");
        return 1;
    }

    Py_Initialize();

    //create faux-module containing C++ methods for access by python scripts
    Py_InitModule("test_embed", EmbMethods);

    pName = PyString_FromString(argv[1]);
    /* Error checking of pName left out */

    pModule = PyImport_Import(pName);
    Py_DECREF(pName);

    if (pModule != NULL) {
        pFunc = PyObject_GetAttrString(pModule, argv[2]);
        /* pFunc is a new reference */

        if (pFunc && PyCallable_Check(pFunc)) {
            pArgs = PyTuple_New(argc - 3);
            for (i = 0; i < argc - 3; ++i) {
                pValue = PyInt_FromLong(atoi(argv[i + 3]));
                if (!pValue) {
                    Py_DECREF(pArgs);
                    Py_DECREF(pModule);
                    fprintf(stderr, "Cannot convert argument\n");
                    return 1;
                }
                /* pValue reference stolen here: */
                PyTuple_SetItem(pArgs, i, pValue);
            }
            pValue = PyObject_CallObject(pFunc, pArgs);
            Py_DECREF(pArgs);
            if (pValue != NULL) {
                printf("Result of call: %ld\n", PyInt_AsLong(pValue));
                Py_DECREF(pValue);
            }
            else {
                Py_DECREF(pFunc);
                Py_DECREF(pModule);
                PyErr_Print();
                fprintf(stderr,"Call failed\n");
                return 1;
            }
        }
        else {
            if (PyErr_Occurred())
                PyErr_Print();
            fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]);
        }
        Py_XDECREF(pFunc);
        Py_DECREF(pModule);
    }
    else {
        PyErr_Print();
        fprintf(stderr, "Failed to load \"%s\"\n", argv[1]);
        return 1;
    }
    Py_Finalize();
    return 0;

}