如何每n秒运行一个耗时的进程？

Question

I need to run a process every n seconds. I figured Threading.timer is the best way to do it. But when i run my command it doesn't run every n second, but starts running over and over, in a lot less time than the given n and loops unstoppable. Here is my code:

#!/usr/bin/python

import threading
import time

brake = 10
k = int(5)

def printit():
    for x in range(k):
        threading.Timer((int(brake)), printit).start()
        print "Hello World!"  
        #i have a longer process here, it takes a few seconds to run
        #i give more than double of the time needed to run it
printit()

So what I want to happen is: It prints Hello world 5 times with 10 seconds brake between each. But instead it prints it a lot faster and doesn't stop. Am I missing some parameters, or is the problem with the process I am trying to run? I also appreciate any other, simpler methods to run the proess every n seconds.

Answer 1

While you appear to be using python2.x (print as a keyword) and thus sleep is a good idea, if you are using py3.4 onwards there is asyncio

import asyncio

def do_task(end_time, loop):
    print('hello world!')
    if (loop.time() + 1.0) < end_time:
        loop.call_later(1, do_task, end_time, loop)
    else:
        loop.stop()

loop = asyncio.get_event_loop()

end_time = loop.time() + 10.0
loop.call_soon(do_task, end_time, loop)

loop.run_forever()
loop.close()

Answer 2

You can do it just with time in python

import time

k = int(5)

def printit():
    for x in range(k):
        time.sleep(5)
        print "Hello World!"
        #i have a longer process here, it takes a few seconds to run
        #i give more than double of the time needed to run it
printit()

Answer 3

You really want to pause for 10 seconds.

time.sleep(brake)

If you did want a timer approach to run all of your operations in a separate thread. You need to separate your print function from the timer function. However, this will print "Hello World!" 5 times all at the same time after 10 seconds has passed.

import threading
import time

brake = 10
k = 5

def printit():
    for x in range(k):
        threading.Timer(brake, long_process, args=('Hello World!',)).start()

def long_process(item):
    print(item)
    #i have a longer process here, it takes a few seconds to run
    #i give more than double of the time needed to run it


printit()

Answer 4

Thanks for all the answers, but in the mean time I figured out the perfect way to do it:

import time

a=2
b=5

for x in range(a):
    start = time.time()
    print "Hello World!"
    time.sleep(3)
    run = (-(start)+time.time())
    time.sleep(int(b)-(run))

Its the only way I know to run a process REPEATEDLY every n seconds. It could be done a lot easier simply with time.sleep, but if you have a longer process, you need to reduce the sleeping time by the time your process took to run.