Python Integration w/ C

README.md

Two things we can do with C and Python integration.

1. C Extensions for Python

   In other words, we can write python methods in pure C.

2. Embedding Python a

The reasons for doing #1 are obvious because we can make speed improvements. For #2, it is due to transporting Python libraries over to C.

Compilation

Compilation is a bit more challenging because we have to do something like:

gcc -I /usr/local/opt/python@3.7/Frameworks/Python.framework/Versions/3.7/include/python3.7m hello.c -o hello

However, we can actually utilize a hidden utility python seems to be hiding from us called "python-config." As long as you can find where Python is installed, you can find the necessary directories. With python-config, you can do this instead:

# Double dollar sign is used to differentiate syntax usage if you use this in a Makefile 
gcc $$(/usr/local/opt/python@3.7/Frameworks/Python.framework/Versions/3.7/bin/python3.7-config --cflags) hello.c -o hello
#./hello

The embedded version requires further options so we have to add --embed and --ldflags to make things easier.

gcc $$(/opt/homebrew/Cellar/python@3.8/3.8.15/Frameworks/Python.framework/Versions/3.8/bin/python3.8-config --cflags --ldflags --embed) embedded.c -o embedded
./embedded

cmodule.c

// Example C extension which ends up being a Python method you can call.
#include <Python.h>
int Cfib(int n) {
    if (n < 2)
        return n;
    else
        return Cfib(n - 1) + Cfib(n - 2);
}

static PyObject* fib(PyObject* self, PyObject* args) {
    int n;
    if (!PyArg_ParseTuple(args, "i", &n))
        return NULL;
    return Py_BuildValue("i", Cfib(n));
}

static PyMethodDef myMethods[] = {
    {"fib", fib, METH_VARARGS, "Calculates the fibonacci numbers"},
    {NULL, NULL, 0, NULL} // wat
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT,
    "cmodule",        /* m_name */
    "Fib Module",         /* m_doc */
    -1,                 /* m_size */
    myMethods,   /* m_methods */
//    NULL,               /* m_reload */
//    NULL,               /* m_traverse */
//    NULL,               /* m_clear*/
//    NULL,               /* m_free */
};

PyMODINIT_FUNC PyInit_cmodule(void)
{
    return PyModule_Create(&module);
}

int main() {
   // printf() displays the string inside quotation
   printf("Hello, Fibonacci World!\n");
   return 0;
}

embedded.c

// Example Python embedded inside a C/C++ file.
#define PY_SSIZE_T_CLEAN
#include <Python.h>

int
main(int argc, char *argv[])
{
    wchar_t *program = Py_DecodeLocale(argv[0], NULL);
    if (program == NULL) {
        fprintf(stderr, "Fatal error: cannot decode argv[0]\n");
        exit(1);
    }
    Py_SetProgramName(program);  /* optional but recommended */
    Py_Initialize();
    PyRun_SimpleString("from time import time,ctime\n"
                       "print('Today is', ctime(time()))\n");
    if (Py_FinalizeEx() < 0) {
        exit(120);
    }
    PyMem_RawFree(program);
    return 0;
}