Embedding Python into C example not working

Question

I'm following this tutorial on Embedding Python on C, but their Pure Embedding example is not working for me.

I have on the same folder (taken from the example):

call.c

#include <Python.h>

int
main(int argc, char *argv[])
{
    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();
    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;
}

multiply.py

def multiply(a,b):
    print "Will compute", a, "times", b
    c = 0
    for i in range(0, a):
        c = c + b
    return c

And I compile and run like this:

$ gcc $(python-config --cflags) call.c $(python-config --ldflags) -o call
call.c: In function ‘main’:
call.c:6:33: warning: unused variable ‘pDict’ [-Wunused-variable]
     PyObject *pName, *pModule, *pDict, *pFunc;
                                 ^
# This seems OK because it's true that pDict is not used

$ ./call multiply multiply 3 2
ImportError: No module named multiply
Failed to load "multiply"

Why can't it load multiply module? Example doesn't show filenames nor paths. Can it be a path problem?

Thanks a lot.

Can you import that module from the interactive interpreter? python -c 'import multiply'? If you have python3 installed then you are probably getting a SyntaxError when trying to import that module. — Bakuriu
– Bakuriu, Commented Apr 22, 2014 at 14:05

Roberto Reale · Accepted Answer · 2014-04-22 14:00:25Z

4

Try setting PYTHONPATH:

export PYTHONPATH=`pwd`

answered Apr 22, 2014 at 14:00

Roberto Reale

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1 Comment

Bakuriu Over a year ago

Note that this will break if you change directory. You can launch the program as: PYTHONPATH=. ./call multiply multiply 3 2 and the call program will receive the redefined PYTHONPATH variable in its environment.

eljefedelrodeodeljefe · Accepted Answer · 2015-10-22 18:23:16Z

0

Really, the example should have PySys_SetPath("."); after initialization.

answered Oct 22, 2015 at 18:23

eljefedelrodeodeljefe

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