How to run a program periodically by using Python

[excite]

I want to run a function periodically by using Python, and I found that
time.sleep() may be of help, however, I think it may not be safe and flexible. Can somebody give me some suggestions on it? Thanks.

[bartonc]

I want to run a function periodically by using Python, and I found that
time.sleep() may be of help, however, I think it may not be safe and flexible. Can somebody give me some suggestions on it? Thanks.

The Python 2.4.4 docs say: "The actual suspension time may be less than that requested because any caught signal will terminate the sleep() following execution of that signal's catching routine. Also, the suspension time may be longer than requested by an arbitrary amount because of the scheduling of other activity in the system".
Please tell us more about your application - there may be better ways of doing this. So tell us: Does you app have a GUI? How often is "periodically"? What operating system are you running? Any other details about the function you want to run. Keep posting,
Barton

[excite]

The Python 2.4.4 docs say: "The actual suspension time may be less than that requested because any caught signal will terminate the sleep() following execution of that signal's catching routine. Also, the suspension time may be longer than requested by an arbitrary amount because of the scheduling of other activity in the system".
Please tell us more about your application - there may be better ways of doing this. So tell us: Does you app have a GUI? How often is "periodically"? What operating system are you running? Any other details about the function you want to run. Keep posting,
Barton

Thanks. The program does not have a GUI, running on a windows system, and I would like to run some functions every hour. The current programs are written in both C and python language, and I packed all the files by Python. Actually, the input files of my programs will be updated every hour externally, so I can run the functions after I detect the input files have been modified. However, if something wrong and the input files have not been updated in some hour, the program will lose synchronization. So I still need to know the time, and run the functions in each hour even the input files have not been updated.

[bartonc]

I've got a few ideas that I'll work up for you.

Anybody else?

[Subsciber123]

How about something like this:

import time
next_time=time.time()
while True:
    hourly_function()
    next_time=(next_time+3600) #sets the next occurrence of the
                                   #function to 1 hour later
    while True:
        sleep(60)             #sleeps for a minute
        if time.time()>next_time:
            break
 

This code will not work, however, for more than a day or so, and is only accurate to within about a minute.

[excite]

How about something like this:

import time
next_time=time.time()
while True:
    hourly_function()
    next_time=(next_time+3600) #sets the next occurrence of the
                                   #function to 1 hour later
    while True:
        sleep(60)             #sleeps for a minute
        if time.time()>next_time:
            break
 

This code will not work, however, for more than a day or so, and is only accurate to within about a minute.

Thanks. But why this code will not work for more than a day? Does the timer will be initialized every day? (Sorry that I am not very good at Python, I will check it later). If it is true, I think I can put the "next_time=time.time()" into the first while block, like this:

import time
while True:
    next_time=time.time()
    hourly_function()
    next_time=(next_time+3600) #sets the next occurrence of the
                                   #function to 1 hour later
    while True:
        sleep(60)             #sleeps for a minute
        if time.time()>next_time:
            break
 

What do you think of it?

[fuffens]

On a linux/unix system I would always use Cron for periodic tasks like this instead of running your own Python script to control execution of other Python scripts and c-programs. There are several implementations of Cron on Windows also. Just Google for cron and windows (http://www.cronforwindows.com/ for example).

BR
/Fredrik