with keyboard.Listener(on_press=on_press, on_release=on_release) as listener:
    listener.join()

with keyboard.Listener(on_press=on_press, on_release=on_release) as listener:

    # ... your code ...

    listener.join()

listener = keyboard.Listener(on_press=on_press, on_release=on_release)
listener.start()

# ... your code ...

listener.stop()

import tkinter as tk
from pynput.keyboard import Listener, Key

# --- functions ---

def on_press(key): # `key` can be `Key` (which doesn't have `char`) or `KeyCode` (which have `char`)
    global listen 

    #print(str(key) == "'1'", str(key))

    #if key == Key.esc:
    if str(key) == 'Key.esc':
        listen = not listen

    if listen:
        #if hasattr(key, 'char') and key.char == '1': # there is no `Key.1` and `1` 
        if str(key) == "'1'": # it needs `' '` in string
            label_var.set(label_var.get()+'1')
            print('1!')

# --- main ---

listen = False

root = tk.Tk()

label_var = tk.StringVar()

label = tk.Label(root, textvariable=label_var, width=10)
label.pack()

# create listener without starting 
listener = Listener(on_press=on_press)

print('start')
listener.start()
#listener.wait()

print('mainloop')
root.mainloop()

print('stop')
listener.stop()

print('end')
# without `listener.join()` because it runs as `daemon`