I'd recommend .XCompose

The start method from pynput's keyboard listener joins the listener with the current thread. So just call it in the thread that starts the Kivy application.

from kivy.app import App
from kivy.uix.label import Label
from pynput.keyboard import Listener


def on_press(key):
    print(f"Key press was listened to from Kivy event loop! Key pressed: {key}")


class TestApp(App):
    def build(self):
        return Label(text="Check console to witness keyboard being listened to")
    
    def run(self):
        Listener(on_press=on_press).start()
        super().run()


if __name__ == "__main__":
    TestApp().run()

As per two comments directly above, IN order to keep focus on the pygame window (effectively keep the cursor within the bounds of the pygame window until a I was able to make this work with the following code:

pygame.event.set_grab(True) # Keeps the cursor within the pygame window

Combine this code with a way to quit the program with a key press such as the ESCAPE key (since it will be impossible to close the window by moving your cursor to the frame of the window to close it that way by pygame.QUIT):

run = True
while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
            run = False

I am currently working on a similar problem. I got an idea how to solve this. But did not try it yet. Not sure if I should put this into a new question.

• set up a virtual console that automatically logs in a user
• this console does not show an interactive shell (bash) but just a process that listens for key-presses and sends them to MPD

That's it. You still may switch to a standard console using Ctrl-Fx and then log-in normally without any side effects like unwanted control of the MPD.

There are still several problems unsolved:

• does linux open up the virtual consoles at all if there is no monitor attached?

• how to set up this console? /etc/login.defs?

• what language and library to use for the listener process (I implemented everything in python until now)

• how to pass the events to MPD. (through mpc command line client or python mpc client library?)

I marked this as community wiki. So anybody feel free to contribute to this answer.

Background: I implemented a headless audio-player using MPD on raspberry pi that currently is controlled via GPIO pins. Now I would like to be able to control it via keyboard as well.

pyHook seems like it would work well for this (mentioned by furas)

from pyHook import HookManager
from win32gui import PumpMessages, PostQuitMessage

class Keystroke_Watcher(object):
    def __init__(self):
        self.hm = HookManager()
        self.hm.KeyDown = self.on_keyboard_event
        self.hm.HookKeyboard()


    def on_keyboard_event(self, event):
        try:
            if event.KeyID  == keycode_youre_looking_for:
                self.your_method()
        finally:
            return True

    def your_method(self):
        pass

    def shutdown(self):
        PostQuitMessage(0)
        self.hm.UnhookKeyboard()


watcher = Keystroke_Watcher()
PumpMessages()