0 Python embed example.md

Python embed example

main.cpp

// g++ $(python3-config --embed --libs --ldflags --cflags ) main.cpp
#include <Python.h>
#include <string>

int main(void) {

    PyStatus st;
    PyConfig cfg;
    PyConfig_InitPythonConfig(&cfg);   // normal mode using env vars

    const char *ve = getenv("VIRTUAL_ENV");
    if (ve && *ve) {
        char exe[4096];
        snprintf(exe, sizeof(exe), "%s"
        #ifdef _WIN32
            "\\Scripts\\python.exe"
        #else
            "/bin/python3"
        #endif
        , ve);

        wchar_t *wexe = Py_DecodeLocale(exe, NULL);
        if (!wexe) return 1;

        PyConfig_SetString(&cfg, &cfg.program_name, wexe);
        PyConfig_SetString(&cfg, &cfg.executable,   wexe);
        PyMem_RawFree(wexe);

        cfg.site_import = 1; 
    }

    st = Py_InitializeFromConfig(&cfg);
    PyConfig_Clear(&cfg);
    if (PyStatus_Exception(st)) {
        Py_ExitStatusException(st);
    }

    // begin user code
    const char *py_code =
        "def get_pi():\n"
        "    import math\n"
        "    return math.pi\n";

    if (PyRun_SimpleString(py_code) != 0) {
        fprintf(stderr, "Failed to run embedded python code\n");
        if (PyErr_Occurred()) PyErr_Print();
        Py_Finalize();
        return 1;
    }

    PyObject *main_mod = PyImport_AddModule("__main__"); // borrowed reference
    if (!main_mod) {
        fprintf(stderr, "Cannot get __main__ module\n");
        if (PyErr_Occurred()) PyErr_Print();
        Py_Finalize();
        return 1;
    }

    PyObject *func = PyObject_GetAttrString(main_mod, "get_pi");
    if (!func || !PyCallable_Check(func)) {
        fprintf(stderr, "get_pi is not found or not callable\n");
        if (PyErr_Occurred()) PyErr_Print();
        Py_XDECREF(func);
        Py_Finalize();
        return 1;
    }

    PyObject *result = PyObject_CallObject(func, NULL);
    Py_DECREF(func);

    if (!result) {
        fprintf(stderr, "call to get_pi() failed\n");
        if (PyErr_Occurred()) PyErr_Print();
        Py_Finalize();
        return 1;
    }

    double pi_val = PyFloat_AsDouble(result);
    if (PyErr_Occurred()) {
        fprintf(stderr, "Failed to convert result to double\n");
        PyErr_Print();
        Py_DECREF(result);
        Py_Finalize();
        return 1;
    }

    printf("pi = %.15g\n", pi_val);

    Py_DECREF(result);
    // end user code

    Py_Finalize();
    return 0;
}