In official Doc. of Python 3, there is a short introduction to embedding Python in another application like C/C++ (see).

The common procedure is as follows,

1. write prototype C/C++ code and Python module codes.
   Note that in the Python codes conventions of python 2 & 3 can not be mixed together, which may cause segfault when running.

call.c

#include 
    
     intmain(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_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 = 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;}
    

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

1. For a single C code, just build like

g++ call.c -o call `python3-config --cflags` `python3-config --ldflags`

This can be written as a shell like build.sh.

3. To run the code, write a shell named run.sh,

PYTHONPATH=. ./call multiply multiply 3 2

Here call is the main code, the two multiplys are the module and function names, respectively.

When running, this code gives,

Will compute 3 times 2Result of call: 6

Note if no PYTHONPATH=. statement in front of the run command, there will be errors like ImportError: No module named multiply.

Someone suggested to add into the .py file

import syssys.path.insert(0, "./path/to/your/modules/")

I tested but not helpful.

BTW, the system path can be checked by

import sysprint(sys.path)

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Useful commands in Python 3 are:

PyObject *exc_type = NULL, *exc_value = NULL, *exc_tb = NULL;PyErr_Fetch(&exc_type, &exc_value, &exc_tb);PyObject* str_exc_type = PyObject_Repr(exc_type); //Now a unicodeobjectPyObject* pyStr = PyUnicode_AsEncodedString(str_exc_type, "utf-8","Error ~");const char *strExcType = PyBytes_AS_STRING(pyStr);Py_XDECREF(str_exc_type);Py_XDECREF(pyStr);Py_XDECREF(exc_type);Py_XDECREF(exc_value);Py_XDECREF(exc_tb);

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Other useful tutorials are