AppKit not dynamically sensing the Frontmost App

Well, I'm not all that familiar with Python (I'm a Ruby guy), but various scripting languages have been extended to provide access (bridges) to the Cocoa APIs. You must be running one of those (such as PyObjC) to be able to import stuff from the AppKit.

Since it deals with the user interface, AppKit is designed to work with a run loop - that is, the system periodically loops through the various UI objects and passes events (clicks, drags, keys, etc) on to those applications that are interested in them. In your case, NSWorkspace.sharedWorkspace checks for workspace events such as when applications change, and makes that information available either through notifications or its class methods.

The while loop you are using is not letting the system access events (assuming you even have a run loop), so your information is not getting updated. Note that even in a Cocoa application this kind of practice will result in the UI getting blocked. The solution is to allow the system to process events, either through normal "gaps" in the execution of your code, or by manually providing a means to do so.

I saw your code early this morning but have been traveling all day. The following code will print out the current frontmost application that I click on whether that is Safari, Sublime Text 3, or Terminal, which were the applications I tested it with on macOS High Sierra 10.13.6 (17G65).

This is the System Python 2.7.10. The Python-Objective-C bridge is available by default in Python when you import that appropriate Class library. Ideally the following code should be within a delegate that responds to events, but keeping it simple:

There is an implicit "PyObjC" that Apple has enabled in the System Python, but does not exist in any user added Python flavors. For non-Apple System Python, one uses this PyObjC solution — maybe — depending on its compatibility with the Python version in use. I have not used it.

Which Python bridge are you using, PyObjC?

Well, if you are indeed using PyObjC, you might take a look at the examples on their Work with Appkit page.

You are welcome.

You do not need to import NSApplicationActivateIgnoringOtherApps, but rather just the following:

from Cocoa import NSApplication

or

from AppKit import NSApplication.

When you import NSApplication class, you get all of its methods for free without a need for their declaration:

Keeping everything in a tight loop like that doesn't let the system process events (a GUI wouldn't be responsive, either) - what kind of runloop are you using?