Python - Tkinter - Catch two digits number

import tkinter as tk

''' catch two (or more) keys pressed in short time and tread it as one text '''

# --- functions ---

# keys buffer
keybuf = []


def test_after():

    # check if buffer is not empty
    if keybuf:

        # get all keys in buffer as one text
        text = ''.join(keybuf)

        # clear buffer
        keybuf.clear()

        # run some function here
        print('after:', text)


def get_key(event):

    # save key in buffer
    keybuf.append(event.char)

    # check buffer after 500ms (0.5s)
    root.after(500, test_after)

# --- main ---

root = tk.Tk()

root.bind('<Key>', get_key)

root.mainloop()