Python Swift Interoperability using ctypes

callbackTest.swift

private var callback: ((Int)->Void)? = nil
private let number: Int = 123

@_silgen_name("set_callback")
public func setCallback(pointerToCTypesFunction: UnsafeMutablePointer<(Int)->Void>) {
    print("swift: setting callback")
    callback = pointerToCTypesFunction.pointee
}

@_silgen_name("execute_callback")
public func executeCallback() {
    if let callback = callback {
        print("swift: executing callback with number ", number)
        callback(number)
    } else {
        print("swift: no callback was set")
    }
}

native_callback_test.py

from ctypes import *

native_lib = CDLL('./libCallbackTest')

@CFUNCTYPE(None, POINTER(c_int))
def callback(number):
    print('python: the number is ', number[0])

native_lib.set_callback(byref(callback))

native_lib.execute_callback()

SwiftPythonCTypes.md

Python Swift Interoperability using ctypes

A demo on how to call swift code from python and call back python code from swift.

Run on macOS or Linux

• Put both files into the same directory
• run swiftc -emit-library -o ./libCallbackTest callbackTest.swift to build a shared library from swift code
• run python native_callback_test.py to execute the python script