How to use Swift dylib in Python Project in macOS?

Question

I've simple Swift package created by using command

cd Desktop

mkdir AICore

cd AICore

swift package init --type library

and edited the configuration to dynamic library configuration like below,

Package.Swift

// swift-tools-version: 5.6
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "AICore",
    platforms: [.macOS(.v10_15)],
    
    products: [  
        .library(name: "AICore", type: .dynamic, targets: ["AICore"]),
    ],
    dependencies: [
    ],
    targets: [
        .target(
            name: "AICore",
            dependencies: [])
    ]
)

AICore.swift:

import Cocoa
 
public func launchMyAppKitWindow() {
    let app = NSApplication.shared
    let window = NSWindow(contentRect: NSRect(x: 0, y: 0, width: 400, height: 300), styleMask: [.titled, .closable, .resizable], backing: .buffered, defer: false)
    window.center()
    window.title = "My AppKit Window"
    window.makeKeyAndOrderFront(nil)
    app.run()
}

Project Structure:

├── AICore
│   ├── Package.swift
│   ├── README.md
│   └── Sources
│       └── AICore
│           └── AICore.swift
└── Test
    ├── libAICore.dylib
    └── main.py

I've compiled my swift program using swift build and I've unhided the hidden build folder inside AICore parent folder. The library is locating at build->x86_64-apple-macosx->libAICore.dylib

I copied the library and pasted to Test folder which has below python script to test.

import ctypes
# https://docs.python.org/3/library/ctypes.html
# Load the dylib
my_appkit_lib = ctypes.CDLL("/Users/YxT2/Desktop/PY/Test/libAICore.dylib")

# Call the launch function
my_appkit_lib.launchMyAppKitWindow()

I run the code using the command python3 main.py and got below error

Traceback (most recent call last):
  File "/Users/YxT2/Desktop/PY/Test/main.py", line 7, in <module>
    my_appkit_lib.launchMyAppKitWindow()
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/[email protected]/3.11.3/Frameworks/Python.framework/Versions/3.11/lib/python3.11/ctypes/__init__.py", line 389, in __getattr__
    func = self.__getitem__(name)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/Cellar/[email protected]/3.11.3/Frameworks/Python.framework/Versions/3.11/lib/python3.11/ctypes/__init__.py", line 394, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: dlsym(0x21db45be0, launchMyAppKitWindow): symbol not found

I tested my swift code which is actually launching the window show in below screenshot.

But I want to use this test library to python code to call launchMyAppKitWindow function written in Swift, Can anyone help me to resolve this issue?

Answer 1

1. Swift functions are not directly accessible from Python because Swift uses a different Application Binary Interface (ABI). To make the function accessible, you should mark it with the @_cdecl attribute to use the C ABI. Modify your AICore.swift like this:

    import Cocoa
    
    @_cdecl("launchMyAppKitWindow")
    public func launchMyAppKitWindow() {
      ...
    }

2. Compile AICore.swift. Note: OS X "libAICore.dylib"

   # creates "libXXX.so" (or on OS X, "libAICore.dylib")
   swiftc -emit-library AICore.swift 
   
   
   
   

(Above image is taken from https://gist.github.com/jiaaro/e111f0f64d0cdb8aca38)

3. The path in main.py - Check the library path.

   -- error in this line --

my_appkit_lib = ctypes.CDLL("/Users/YxT2/Desktop/PY/Test/libAICore.dylib")