import threading
def 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.py
hello world
hello world
hello 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 args
if __name__ == "__main__":
    t = CountDownExec(3, myAction, ["hello", "world"])
    t.start()