Undeclared identifier: PyUnicode_DecodeFSDefault

Question

I try to compile the example code from Python website https://docs.python.org/3/extending/embedding.html. Everything works fine except the following line:

 pName = PyUnicode_DecodeFSDefault(argv[1]);

I have Python 3.6 installed on my MacOS El Captain. My make file looks like the following:

call_function:     call_function.o        
    gcc -o call_function call_function.o -export-dynamic -L/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/config-3.6m-darwin -lpython3.6m -lpthread -lm -ldl -lutil


call_function.o:call_function.cpp    
    gcc -c call_function.cpp -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m

When I compile the C++ code, I get the following error:

gcc -c call_function.cpp -I/Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m
call_function.cpp:16:13: error: use of undeclared identifier    'PyUnicode_DecodeFSDefault'
pName = PyUnicode_DecodeFSDefault(argv[1]);
        ^
1 error generated.

Does anyone know how to fix the above error? I would greatly appreciated for your help.

Here is the complete example code:

#include <Python/Python.h>
#include <Python/unicodeobject.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 = PyUnicode_DecodeFSDefault(argv[1]);
// pName = PyUnicode_FromString(argv[1]);  <-- also gives me an error

/* 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 = PyLong_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", PyLong_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;
}

Answer 1

I figure out what the problem is. The include <Python/Python.h> statement is actually linked to /System/Library/Frameworks/Python.framework/Versions/Current which currently is Python2.7. I have installed Python 3.6 on my Mac and even I include /Library/Frameworks/Python.framework/Versions/3.6/include/python3.6m in my make file, it's still referred to the Python.h file in MacOS's Python 2.7 folder. I tried to change the symbolic link of the Current to the new 3.6 folder and it's not letting me make the changes. Does anybody know how to change the symbolic link of the Python2.7 current folder so my gcc would look into the Python 3.6 folder for Python.h instead?

Answer 2

It is been a long time since this question got posted, but the solution that I came up is as follows,

char * full_cls_name = argv[1];
Py_Initialize();
pName = PyString_FromString(full_cls_name);

You should also check whether argv[1] exists or not?