Get currently focused OS X application in python

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Ever wanted to programmatically find out what OS X application you have running at any given time? This post will quickly detail how it is done.

Title Image: Get currently focused OS X application in python

Basically the crux of it is using Apple’s AppKit bindings in python, specifically the NSWorkspace module of AppKit.

Basic example

At the very least, this is how you read the application name, and get its associated icon.

from AppKit import NSWorkspace

app = NSWorkspace.sharedWorkspace().activeApplication()
if app:
    app_name = app['NSApplicationName']
    icon = app['NSWorkspaceApplicationKey'].icon()

As a module

If you just want a simple module you can use in your app, you could dump this into a python file and import it. Essentially all it does is returns a dict with the app name and a PIL TIFF image object that you can do whatever you want with. It also raises a custom Exception if the app lookup failed for any reason.

"""Module to get the currently focused app in OS X."""
from AppKit import NSWorkspace
from PIL import Image
import StringIO


class AppLoadFailedException(RuntimeError):
    """Custom exception for failing to load App information."""

    pass


def current_app():
    """Fetch the currently focused app."""
    app = NSWorkspace.sharedWorkspace().activeApplication()
    if app:
        app_name = app['NSApplicationName']
        icon = app['NSWorkspaceApplicationKey'].icon()
        # convert the icon to tiff, then return PIL image
        tiffdata = icon.TIFFRepresentation()
        img = Image.open(StringIO.StringIO(tiffdata))
        return dict(name=app_name, image=img)
    raise AppLoadFailedException('Failed to load app information.')

Putting it together

Save the module code into currentapp.py, or whatver you want to call it, and then import it.

import currentapp

try:
    print currentapp.current_app()
except currentapp.AppLoadFailedException as error:
    # handle specific error here
    print error
except Exception as error:
    # handle generic exception here
    print error

Saving the icon

Now that you are fetching the app data and icon from NSWorkspace, you most likely want to save the image somewhere. This is pretty straight forward, we simply just use PILs .save() call. Additionally you can also thumbnail it (as the original icon is 1024x1024) as I have done below. For the sake of brevity, I have removed the include & exception handling code.

ca = currentapp.current_app()
size = 128,128
ca.image.thumbnail(size, Image.ANTIALIAS)
ca.image.save('path/to/filename.png', 'PNG')

As always, hit me up on twitter if you have any questions/comments.

Written on 28 May 2016