Schedule a repeating event in Python 3

I'm trying to schedule a repeating event to run every minute in Python 3.

I've seen class sched.scheduler but I'm wondering if there's another way to do it. I've heard mentions I could use multiple threads for this, which I wouldn't mind doing.

I'm basically requesting some JSON and then parsing it; its value changes over time.

To use sched.scheduler I have to create a loop to request it to schedule the even to run for one hour:

scheduler = sched.scheduler(time.time, time.sleep)

# Schedule the event. THIS IS UGLY!
for i in range(60):
    scheduler.enter(3600 * i, 1, query_rate_limit, ())

scheduler.run()

What other ways to do this are there?

You could use threading.Timer, but that also schedules a one-off event, similarly to the .enter method of scheduler objects.

The normal pattern (in any language) to transform a one-off scheduler into a periodic scheduler is to have each event re-schedule itself at the specified interval. For example, with sched, I would not use a loop like you're doing, but rather something like:

def periodic(scheduler, interval, action, actionargs=()):
    scheduler.enter(interval, 1, periodic,
                    (scheduler, interval, action, actionargs))
    action(*actionargs)

and initiate the whole "forever periodic schedule" with a call

periodic(scheduler, 3600, query_rate_limit)

Or, I could use threading.Timer instead of scheduler.enter, but the pattern's quite similar.

If you need a more refined variation (e.g., stop the periodic rescheduling at a given time or upon certain conditions), that's not too hard to accomodate with a few extra parameters.

You could use schedule. It works on Python 2.7 and 3.3 and is rather lightweight:

import schedule
import time

def job():
   print("I'm working...")

schedule.every(10).minutes.do(job)
schedule.every().hour.do(job)
schedule.every().day.at("10:30").do(job)

while 1:
   schedule.run_pending()
   time.sleep(1)

My humble take on the subject:

from threading import Timer

class RepeatedTimer(object):
    def __init__(self, interval, function, *args, **kwargs):
        self._timer     = None
        self.function   = function
        self.interval   = interval
        self.args       = args
        self.kwargs     = kwargs
        self.is_running = False
        self.start()

    def _run(self):
        self.is_running = False
        self.start()
        self.function(*self.args, **self.kwargs)

    def start(self):
        if not self.is_running:
            self._timer = Timer(self.interval, self._run)
            self._timer.start()
            self.is_running = True

    def stop(self):
        self._timer.cancel()
        self.is_running = False

Usage:

from time import sleep

def hello(name):
    print "Hello %s!" % name

print "starting..."
rt = RepeatedTimer(1, hello, "World") # it auto-starts, no need of rt.start()
try:
    sleep(5) # your long-running job goes here...
finally:
    rt.stop() # better in a try/finally block to make sure the program ends!

Features:

• Standard library only, no external dependencies
• Uses the pattern suggested by Alex Martnelli
• start() and stop() are safe to call multiple times even if the timer has already started/stopped
• function to be called can have positional and named arguments
• You can change interval anytime, it will be effective after next run. Same for args, kwargs and even function!

Based on MestreLion answer, it solve a little problem with multithreading:

from threading import Timer, Lock


class Periodic(object):
    """
    A periodic task running in threading.Timers
    """

    def __init__(self, interval, function, *args, **kwargs):
        self._lock = Lock()
        self._timer = None
        self.function = function
        self.interval = interval
        self.args = args
        self.kwargs = kwargs
        self._stopped = True
        if kwargs.pop('autostart', True):
            self.start()

    def start(self, from_run=False):
        self._lock.acquire()
        if from_run or self._stopped:
            self._stopped = False
            self._timer = Timer(self.interval, self._run)
            self._timer.start()
            self._lock.release()

    def _run(self):
        self.start(from_run=True)
        self.function(*self.args, **self.kwargs)

    def stop(self):
        self._lock.acquire()
        self._stopped = True
        self._timer.cancel()
        self._lock.release()

You could use the Advanced Python Scheduler. It even has a cron-like interface.