How can I run a certain function for a specific time in Python?

Question

For example i have function do_something() and I want it to run for exactly 1 second (and not .923 seconds. It won't do. However 0.999 is acceptable.)

However it is very very important that the do_something must exactly run for 1 second. I was thinking of using UNIX time stamp and calculate the seconds. But I am really wondering if Python has a way to do this in a more aesthetic way...

The function do_something() is long-running, and must be interrupted after exactly one second.

Will it take less than one second, always, and you need to pad it? Will it ever take more than one second, and you want to reduce it? — chmullig, Mar 01 '11 at 17:06
Please clarify your question. Do you want to (a) run `do_something` once for exactly 1 second and then interrupt it, or (b) do you want to run `do_something` repeatedly until 1 second has passed, or (c) do you want to run `do_something` repeatedly until 1 second has passed *and* interrupt the most recent execution when 1 second passes? — phooji, Mar 01 '11 at 17:07
no the do_something() function just does something... However it must only do what ever it is doing for only one second. It must cut off what it is doing if it is 1 second. — JohnRoach, Mar 01 '11 at 17:08
@JohnRoach: I've removed the `while` loop from your question because I think it made people think you were after option (b) or (c). — phooji, Mar 01 '11 at 17:25
Possible duplicate of [Timeout on a function call](https://stackoverflow.com/questions/492519/timeout-on-a-function-call) — Smart Manoj, May 08 '19 at 13:06

senderle · Answer 1 · 2012-07-10T13:26:10.960

I gather from comments that there's a while loop in here somewhere. Here's a class that subclasses Thread, based on the source code for _Timer in the threading module. I know you said you decided against threading, but this is just a timer control thread; do_something executes in the main thread. So this should be clean. (Someone correct me if I'm wrong!):

from threading import Thread, Event

class BoolTimer(Thread):
    """A boolean value that toggles after a specified number of seconds:

    bt = BoolTimer(30.0, False)
    bt.start()
    bt.cancel() # prevent the booltimer from toggling if it is still waiting
    """

    def __init__(self, interval, initial_state=True):
        Thread.__init__(self)
        self.interval = interval
        self.state = initial_state
        self.finished = Event()

    def __nonzero__(self):
        return bool(self.state)

    def cancel(self):
        """Stop BoolTimer if it hasn't toggled yet"""
        self.finished.set()

    def run(self):
        self.finished.wait(self.interval)
        if not self.finished.is_set():
            self.state = not self.state
        self.finished.set()

You could use it like this.

import time

def do_something():
    running = BoolTimer(1.0)
    running.start()
    while running:
        print "running"              # Do something more useful here.
        time.sleep(0.05)             # Do it more or less often.
        if not running:              # If you want to interrupt the loop, 
            print "broke!"           # add breakpoints.
            break                    # You could even put this in a
        time.sleep(0.05)             # try, finally block.

do_something()

score 1 · Answer 2 · answered Mar 01 '11 at 17:11

1

The 'sched' module of Python appears suitable:

http://docs.python.org/library/sched.html

Apart from that: Python is not a real-time language nor does it usually run on a real-time OS. So your requirement is kind of questionable.

answered Mar 01 '11 at 17:11

"Python is not a real-time language" I know I know... I hat it when a language is forced fed to me. It really wasn't my choice. I will check sched. It looks promising. – JohnRoach Mar 01 '11 at 17:19
So you are saying basically I should simply schedule my function for each step? – JohnRoach Mar 01 '11 at 17:30

score 0 · Accepted Answer · answered Mar 01 '11 at 17:19

0

This bit of code might work for you. The description sounds like what you want:

http://programming-guides.com/python/timeout-a-function

It relies on the python signal module:

http://docs.python.org/library/signal.html

answered Mar 01 '11 at 17:19

JoshAdel

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Actually, the `signals` module is not unix-only, but the `SIGALRM` signal is. However if you _are_ on unix, this would be a perfect solution. Especially if you don't have control over the contents of `do_something` . – noio Jun 03 '11 at 06:49
unfortunately, the link to the website is broken by now - has been caught by a domain hostage service :( – Henning Aug 21 '15 at 11:57

How can I run a certain function for a specific time in Python?

3 Answers3