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How to Restart Python Script after Exception and Run it Forever

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Here is a simple trick that I used to restart my python script after unhandled exception.

Let’s say I have this simple script called test.py that I want to run forever. It will just wait 2 seconds and throw an error.

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import time
 
time.sleep(2)
raise Exception("Oh oh, this script just died")


I use the following script called forever in the same directory:

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#!/usr/bin/python
from subprocess import Popen
import sys
 
filename = sys.argv[1]
while True:
    print("\nStarting " + filename)
    p = Popen("python " + filename, shell=True)
    p.wait()

It uses python to open test.py as a new subprocess. It does so in an infinite while loop, and whenever test.py fails, the while loop restarts test.py as a new subprocess.

I’ll have to make the forever script executable by running chmod +x forever. Optionally forever script can be moved to some location in the PATH variable, to make it available from anywhere.

Next, I can start my program with:

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./forever test.py

Which will result in the following output:

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Starting test.py
Traceback (most recent call last):
  File "test.py", line 4, in <module>
    raise Exception("Oh oh, this script just died")
Exception: Oh oh, this script just died
 
Starting test.py
Traceback (most recent call last):
  File "test.py", line 4, in <module>
    raise Exception("Oh oh, this script just died")
Exception: Oh oh, this script just died
 
Starting test.py

As you can tell, this script will run repeatedly, until it is killed with ctr+c.


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  1. Thanks for this great tip. I’m trying to output the subprocess script’s print statements to the screen, but so far no success :(. Here’s what I have so far:

    import subprocess
    import sys

    filename = ‘my_script.py’

    while True:
    print(‘Starting ‘ + filename + ‘ …’)
    p = subprocess.Popen(‘python ‘ + filename, shell=True, stdout=subprocess.PIPE)
    (output, err) = p.communicate()
    print(output)
    p.wait()

    It would be awesome if you could point me in the right direction. Thanks!

    Reply