Scheduling a job in Python

Question

I wish to schedule a python script for every 30 minutes. I am currently using the Timer to run the python script but it is not working precisely. I am using Linux. This code works fine on windows but is not working correctly on Linux. It should be triggered after half an hour but it gets triggered within a minute.

from datetime import datetime, timedelta
from threading import Timer
j=1
while True :
          x=datetime.today()    
          y = x + timedelta(minutes=10*j)
          print(y)
          delta_t=y-x
          secs=delta_t.seconds + 1


          def hello_world():
              print ("hello world")
              print("yes)")
    

          t = Timer(secs, hello_world)
          t.start()

          j=j+1`

Can anyone point out the mistake in above code or suggest an alternative to run the python script in linux after every 30 minutes?

Thank you

Please update the indentation of your code. Python is very sensitive to indentation, as are python programmers. — quamrana, Jun 21 '20 at 09:51
Unless there is a specific reason why you want to have a long-running process which mostly sleeps but actively does something periodically, the usual method for doing tasks periodically on Linux is to use `crontab`. This is not internal to python, but rather a way to make the operating system invoke your python script (or any other command) periodically. — alani, Jun 21 '20 at 10:10
An advantage in using a cron job is that you do not need to restart your process manually, for example after the system is rebooted. — alani, Jun 21 '20 at 10:12
On the specifics of your code, you seem to be trying to create an infinite number of (simultaneous) threads. I can reproduce the fact that once you get to a certain number of threads, the timer for the first one finished unexpectedly quickly (in experimentation I found it happens when you reach 145 threads). I don't know if this could be considered a bug in the library, but I don't think it is reasonable for an application to create such a large number of threads. — alani, Jun 21 '20 at 10:28
@alaniwi I tried using the crontab but I dont know why it gives an error - No such file or directory. I tried running the python command line, it works perfectly fine but crontab gives an error. — Nimesh Shahdadpuri, Jun 21 '20 at 11:23
Have a look at this answer: https://stackoverflow.com/a/13151104/8840245 and it's follow up answer: https://stackoverflow.com/a/18906292/8840245, I think they both can solve your problem without using any external library. Cheers! — Mrinal Roy, Jul 08 '20 at 06:51

score 1 · Answer 1 · edited Jul 08 '20 at 11:44

1

You could use Python’s schedule library.

import schedule

def hello_world():
    print ("hello world")
    print("yes)")

schedule.every(30).minutes.do(hello_world)

while True:  

    # Checks whether a scheduled task  

    # is pending to run or not 

    schedule.run_pending()

Further information: https://www.geeksforgeeks.org/python-schedule-library/

edited Jul 08 '20 at 11:44

Mrinal Roy

969
7
12

answered Jun 21 '20 at 10:06

Vate

56
11

Works well, though requires `pip install schedule`. For something using the stdlib, maybe just a simple `time.sleep` in a loop would work, although one would probably want to sleep until 30 minutes after the previous start time, to allow for the execution time of the task itself. – alani Jun 21 '20 at 10:43
@Vate I dont want to install any external library. – Nimesh Shahdadpuri Jun 21 '20 at 11:24

Scheduling a job in Python

1 Answers1