A simple clock under windows os, using python library 'keyboard' to detect hot-key.

clock.py

import keyboard
import time
from tkinter import *

class Clock(Tk):
    def __init__(self, master=None):
        Tk.__init__(self, master)
        self.wm_attributes("-topmost", 1)
        self.createWidgets()

    def tick(self):
        newTime = time.strftime('%H:%M:%S')
        if newTime != self.time:
            self.time = newTime
            self.timeLabel.config(text=self.time)
        self.timeLabel.after(500, self.tick)

    def createWidgets(self):
        self.time = ''
        self.timeLabel = Label(self, font=('times', 20, 'bold'))
        self.timeLabel.pack()
        self.tick()

clock = None
def invokeClock():
    global clock
    print('invoke:', id(clock))
    if clock == None:
        clock = Clock()

keyboard.add_hotkey('ctrl+alt+k', invokeClock)
keyboard.wait()

in linux python2.7, tkinter should be Tkinter