import threadingdef sayhello():    print "hello world"    global t    #Notice: use global variable!    t = threading.Timer(5.0, sayhello)    t.start()t = threading.Timer(5.0, sayhello)t.start()

>python hello.pyhello worldhello worldhello world

class Timer(threading.Thread):    """    very simple but useless timer.    """    def __init__(self, seconds):        self.runTime = seconds        threading.Thread.__init__(self)    def run(self):        time.sleep(self.runTime)        print "Buzzzz!! Time's up!"class CountDownTimer(Timer):    """    a timer that can counts down the seconds.    """    def run(self):        counter = self.runTime        for sec in range(self.runTime):            print counter            time.sleep(1.0)            counter -= 1        print "Done"class CountDownExec(CountDownTimer):    """    a timer that execute an action at the end of the timer run.    """    def __init__(self, seconds, action, args=[]):        self.args = args        self.action = action        CountDownTimer.__init__(self, seconds)    def run(self):        CountDownTimer.run(self)        self.action(self.args)def myAction(args=[]):    print "Performing my action with args:"    print argsif __name__ == "__main__":    t = CountDownExec(3, myAction, ["hello", "world"])    t.start()