Cancellable threading.Timer in Python

Question

I am trying to write a method that counts down to a given time and unless a restart command is given, it will execute the task. But I don't think Python threading.Timer class allows for timer to be cancelable.

import threading

def countdown(action):
    def printText():
        print 'hello!'

    t = threading.Timer(5.0, printText)
    if (action == 'reset'):
        t.cancel()

    t.start()

I know the above code is wrong somehow. Would appreciate some kind guidance over here.

Answer 1

You would call the cancel method after you start the timer:

import time
import threading

def hello():
    print "hello, world"
    time.sleep(2)

t = threading.Timer(3.0, hello)
t.start()
var = 'something'
if var == 'something':
    t.cancel()

You might consider using a while-loop on a Thread, instead of using a Timer.
Here is an example appropriated from Nikolaus Gradwohl's answer to another question:

import threading
import time

class TimerClass(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.event = threading.Event()
        self.count = 10

    def run(self):
        while self.count > 0 and not self.event.is_set():
            print self.count
            self.count -= 1
            self.event.wait(1)

    def stop(self):
        self.event.set()

tmr = TimerClass()
tmr.start()

time.sleep(3)

tmr.stop()