How to create a Cocoa library and use it in python
Question: I've been making a game and the python library I was used is terrible
(Pyglet). I want to try using Cocoa for the OSX version.

I'll be able to figure out using the objects from classes like NSWindow and
NSOpenGLView and then put these objects in my own class for the game loop.

I have no idea how I can use PyObjC to load a dynamic Objective-C library I
can make and then use the class I will make in python to setup the game which
I suppose can be looped by NSTimer.

However, the loop method will also need to call a python method from one of
many python classes. My game consists of many python classes which are used
for different sections of the game (Mapmaker,GameSession,AnacondaGame etc.).
The game loop will need to call a loop method in any of these classes
depending on the current section and pass even information.

PyObjC is "bi-directional" apparently so how is that done?

Alternatively I could create two methods to be called by python and I add the
python code in-between, where the loop is controlled by python.

The "documentation" on the PyObjC website only seem to explain how to use
Cocoa in python and nothing else.

What I can't do is make a fixed GUI with the interface builder because the
library will need to create windows based on the python input to an
initialisation method of my class.

Knowing the syntax of Objective-C isn't a big problem and I can reefer to the
Cocoa documentation to make the objects I require.

Thank you for any help. It will be appreciated very much. I'm sick of using
broken libraries like pygame and pyglet, using the platform specific OS APIs
seems to be the best method to ensure quality.


Answer: PyObjC bridges Python to the Objective-C runtime, so if you create NSObject
subclasses in Python, they'll be accessible from Objective-C code running in
the same process. What this means is that you'll need to encapsulate all of
your Python functionality in a subclass of NSObject that you can access over
the bridge.

The way I'd do this is by having a singleton controller class on the
Objective-C side that has a method like `-(void)pythonReady:(PythonClass
*)pythonObject`, and also handles the loading of the Python code (which
ensures that the controller class exists when your Python code is loaded).
Then, in your Python code, after creating an instance of your PythonClass, you
can call `pythonReady:` on your controller singleton. Then, in `pythonReady:`
on the Objective-C side, you can call whatever methods you need on
`pythonObject`, which will run the code on the Python side.

To load the Python code from your controller class, you can do something like
this:

    
    
    #import <Python/Python.h>
    
    @implementation PythonController (Loading)
    - (void)loadPython {
        NSString *pathToScript = @"/some/path/to/script.py";
        setenv("PYTHONPATH", [@"/some/path/to/" UTF8String], 1);
        Py_SetProgramName("/usr/bin/python");
        Py_Initialize();
        FILE *pyScript = fopen([pathToScript UTF8String], "r");
        int result = PyRun_SimpleFile(pyScript, [[pathToScript lastPathComponent] UTF8String]);
        if (result != 0) { NSLog(@"Loading Python Failed!"); }
    }
    @end
    

Basically, we simply use the Python C API to run the script inside the current
process. The script itself starts the bridge to the runtime in the current
process, where you can then use the Cocoa API to access your controller
singleton.

