Python how to remove delays in threads?

Question

Python

I am making a program that is turned on and off by a specific key on the keyboard (using pynput). I put the keyboard listen loop on the first thread and the action loop on the second thread. The problem is that after running the code, it does not immediately listen to the keyboard, only after 9-10 seconds. And sometimes it refuses to respond to the Esc button, and sometimes it works. How to get rid of delay?

from threading import Thread
from pynput import keyboard
import time

flag = False
kill = False

def on_press(key):
    global flag
    global kill

    if key == keyboard.KeyCode.from_char('a'):
        print('pressed A')
        flag = not flag
    if key == keyboard.Key.esc:
        kill = True
        return False

def thr2():
    print('joining...')
    with keyboard.Listener(on_press=on_press) as listen:
        listen.join()

def thr1():
    while True:
        if kill:
            break
        if flag:
            print('looping....')
            time.sleep(0.4)

if __name__ == "__main__":
    thread1 = Thread(target=thr1)
    thread2 = Thread(target=thr2)
    thread1.start()
    thread2.start()