fib.c

#include <Python.h>

static PyObject * fibonacci_fib(PyObject *self, PyObject *args) {
    int n;
    if (!PyArg_ParseTuple(args, "i", &n)) {
        return NULL;
    }
    int i;
    int a = 0;
    int b = 1;
    int c;
    for (i = 0; i < n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    return PyLong_FromLong(a);
}

static PyMethodDef methods[] = {
    {"fib", fibonacci_fib, METH_VARARGS, "calculate fibonacci numbers"},
    {NULL, NULL, 0, NULL}
};

static struct PyModuleDef fibonacci_module = {
    PyModuleDef_HEAD_INIT,
    "fibonacci_module",
    "calculate fibonacci numbers",
    -1,
    methods
};

PyMODINIT_FUNC PyInit_fibonacci_module(void) {
    return PyModule_Create(&fibonacci_module);
}

int main(int argc, char *argv[]) {
    wchar_t *program = Py_DecodeLocale(argv[0], NULL);
    if (program == NULL) {
        return 1;
    }
    Py_SetProgramName(program);
    PyImport_AppendInittab("fibonacci_module", &PyInit_fibonacci_module);
    Py_Initialize();
    PyImport_ImportModule("fibonacci_module");
    PyRun_SimpleString("import fibonacci_module\nprint(fibonacci_module.fib(30))");
    PyMem_RawFree(program);
    return 0;
}

// bash -c "clang `python3.10-config --cflags` fib.c `python3.10-config --ldflags` -lpython3.10 -o fib"