Is there a way to, for example, print Hello World!
every n seconds?
For example, the program would go through whatever code I had, then once it had been 5 seconds (with time.sleep()
) it would execute that code. I would be using this to update a file though, not print Hello World.
For example:
startrepeat("print('Hello World')", .01) # Repeats print('Hello World') ever .01 seconds
for i in range(5):
print(i)
>> Hello World!
>> 0
>> 1
>> 2
>> Hello World!
>> 3
>> Hello World!
>> 4
This question is related to
python
multithreading
Save yourself a schizophrenic episode and use the Advanced Python scheduler: http://pythonhosted.org/APScheduler
The code is so simple:
from apscheduler.scheduler import Scheduler
sched = Scheduler()
sched.start()
def some_job():
print "Every 10 seconds"
sched.add_interval_job(some_job, seconds = 10)
....
sched.shutdown()
You can start a separate thread whose sole duty is to count for 5 seconds, update the file, repeat. You wouldn't want this separate thread to interfere with your main thread.
Here's a version that doesn't create a new thread every n
seconds:
from threading import Event, Thread
def call_repeatedly(interval, func, *args):
stopped = Event()
def loop():
while not stopped.wait(interval): # the first call is in `interval` secs
func(*args)
Thread(target=loop).start()
return stopped.set
The event is used to stop the repetitions:
cancel_future_calls = call_repeatedly(5, print, "Hello, World")
# do something else here...
cancel_future_calls() # stop future calls
My humble take on the subject, a generalization of Alex Martelli's answer, with start() and stop() control:
from threading import Timer
class RepeatedTimer(object):
def __init__(self, interval, function, *args, **kwargs):
self._timer = None
self.interval = interval
self.function = function
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:
start()
and stop()
are safe to call multiple times even if the timer has already started/stoppedinterval
anytime, it will be effective after next run. Same for args
, kwargs
and even function
!def update():
import time
while True:
print 'Hello World!'
time.sleep(5)
That'll run as a function. The while True:
makes it run forever. You can always take it out of the function if you need.
Here is a simple example compatible with APScheduler 3.00+:
# note that there are many other schedulers available
from apscheduler.schedulers.background import BackgroundScheduler
sched = BackgroundScheduler()
def some_job():
print('Every 10 seconds')
# seconds can be replaced with minutes, hours, or days
sched.add_job(some_job, 'interval', seconds=10)
sched.start()
...
sched.shutdown()
Alternatively, you can use the following. Unlike many of the alternatives, this timer will execute the desired code every n seconds exactly (irrespective of the time it takes for the code to execute). So this is a great option if you cannot afford any drift.
import time
from threading import Event, Thread
class RepeatedTimer:
"""Repeat `function` every `interval` seconds."""
def __init__(self, interval, function, *args, **kwargs):
self.interval = interval
self.function = function
self.args = args
self.kwargs = kwargs
self.start = time.time()
self.event = Event()
self.thread = Thread(target=self._target)
self.thread.start()
def _target(self):
while not self.event.wait(self._time):
self.function(*self.args, **self.kwargs)
@property
def _time(self):
return self.interval - ((time.time() - self.start) % self.interval)
def stop(self):
self.event.set()
self.thread.join()
# start timer
timer = RepeatedTimer(10, print, 'Hello world')
# stop timer
timer.stop()
Source: Stackoverflow.com