Use Python module in Swift OS X app

The answer depends on how complex your Python is going to be, and what you need in return. Super basic example of just using Python through the C interface in Swift (be sure to add Python.framework):

import Python

Py_Initialize()

let a = PyInt_FromLong(1)
let b = PyInt_FromLong(2)
let c = PyNumber_Add(a, b)

let result = PyInt_AsLong(c)
print("Result is \(result)") // will print 'Result is 3'

For something more complicated, it gets more complicated:

import Python

Py_Initialize()

// call urllib.urlopen('http://icanhazip.com').read()
let module = PyImport_Import(PyString_FromString("urllib"))
let urlOpenFunc = PyObject_GetAttrString(module, "urlopen")
if urlOpenFunc != nil && PyCallable_Check(urlOpenFunc) == 1 {
    let args = PyTuple_New(1)
    PyTuple_SetItem(args, 0, PyString_FromString("http://icanhazip.com"))
    let openCall = PyObject_CallObject(urlOpenFunc, args)
    let readCall = PyObject_CallObject(PyObject_GetAttrString(openCall, "read"), nil)
    if readCall != nil {
        if let result = String.fromCString(PyString_AsString(readCall)) {
            print("My IP is \(result)")
        } else {
            print("Failed")
        }
    }
}

If you want to do some serious work in Python, either make sure the interface called by Swift is super-duper simple, or use PyObjC.