Exit() from background function fails in Python

I'm learnig python and doing some simple programming exercises (Python 3.13.2 and VScode 1.97.1)
Here, while a counter runs in the while loop, I'm listening for any key press in the background.
When "z" is pressed the counter should be set to 0, and when"q" is pressed, the program should exit.
Debugging the program, the key press listener is working and checking the keys correctly.
But the sys.exit() function doesn't work. The counter still keeps on counting.
Where am I going wrong?

import sys
from time import sleep
import os
from pynput.keyboard import Key, Listener

def cls():    # clear terminal screen, cross-platform 
  os.system('cls' if os.name=='nt' else 'clear')
    
cnt = 1
def checkKey(key):  # is called, when a key is pressed
  if hasattr(key, 'char'):
    if key.char == 'z':
      global cnt
      cnt = 0
    if key.char == 'q':
      sys.exit()   # is not quitting the program          
  pass

# Non-Blocking Listener
listener = Listener(on_press=checkKey)
listener.start()

cls()
sleep(0.5)


while True:
  print("{0}".format(cnt), end='\r', flush=True)    # print n in the same line, without carriage return and deactivated output buffer
  sleep(0.5)
  cnt += 1

sys.exit() just raises a SystemExit exception. This will only end the thread it was called from, and only if the exception isn't caught.

It's not designed to end every thread in the program, because there isn't really a safe way to do that without the other threads' cooperation. Trying to do that could interrupt arbitrary work and leave corrupted files and other nasty messes.

To handle this safely, you should give your listener a way of communicating to the main thread that the program should be shut down. A threading.Event, for example. The main thread can check the event to determine if it should shut down.