Cancel timer in Python

问题:

I am working on timer class in python and wrote a simple test code for the same. My purpose is to print the "hello world" message 10 times and then cancel the timer once the iterations are done. The problem is I am unable to cancel the timer and code seems to print "hello world" infinitely.

Below is my code:

from threading import Timer

class myclass():
    iteration_count = 0
    heartbeat = 1

    def printMsg(self):
        print "hello world!"

    def start_job(self):

        self.printMsg()

        self.iteration_count = self.iteration_count + 1

        if self.iteration_count == 10:
            Timer(self.heartbeat, self.start_job, ()).cancel()

        Timer(self.heartbeat, self.start_job, ()).start()


m = myclass()
m.start_job()

I am using Python 2.7 Any help would be highly appreciated

回答1:

Try it:

from threading import Timer

class MyClass(object):
    def __init__(self):
        self.iteration_count = 0
        self.heartbeat = 1

    @staticmethod
    def print_msg():
        print "hello world!"

    def start_job(self):
        self.print_msg()
        self.iteration_count += 1

        timer = Timer(
            interval=self.heartbeat,
            function=self.start_job,
        )
        timer.start()

        if self.iteration_count >= 10:
            timer.cancel()

MyClass().start_job()

---

[NOTE]:

Your problem was that you make another Timer() in if condition and .cancel() it.

回答2:

Seems like you start your timer again right after you cancelled it.

If you change your code to return from start_job() when your end-condition is reached it should work.

    if self.iteration_count == 10:
        Timer(self.heartbeat, self.start_job, ()).cancel()
        return

Actually you don't even have to cancel the timer this way, you just don't start a new one, if the condition is reached.

回答3:

cancelmethod is used to stop the created timer before its action has begun, so just return will be ok.

if self.iteration_count == 10:
    return

See Timer Objects

The timer can be stopped (before its action has begun) by calling the cancel() method.

def hello(): 
    print "hello, world"

t = Timer(30.0, hello)
t.start() # will print "hello, world" after 30 seconds

t.cancel() # stop it printing "hello, world"