How can I terminate (without raising another exception) my python script while handling an exception

Question

In my python3 script, I am calling an external program with the subprocess module. When the called program exits with a non-zero status code, a CalledProcessError is thrown. In that case I print an error message and want to terminate the script in the exception handler.

My problem is, that exit() works by throwing a SystemExit exception itself, so I end up with:

During handling of the above exception, another exception occurred:

The script looks similar to this:

try:
    output = subprocess.check_output(["program"])
    return output
except subprocess.CalledProcessError as error:
    print("program returned non-zero exit status", file=sys.stderr)
    exit(error.returncode)

How can I terminate the script without throwing an exception?

Why are you passing the error.returncode to exit() if you don't want it to propagate? — mdurant
– mdurant, Commented Jul 23, 2014 at 19:27
@mdurant I want to signal the exit code to the shell (which called this script). — Wilhelm Schuster
– Wilhelm Schuster, Commented Jul 23, 2014 at 19:40

dano · Accepted Answer · 2014-07-23 19:37:20Z

2

os._exit Would allow you to quit without raising an exception, but I wouldn't recommend that approach, because it exits ungracefully; no cleanup will be done.

You could also tweak your logic of subprocess a bit, so that sys.exit gets called outside of the except block:

try:
    output = subprocess.check_output(["programm"])
    return output
except subprocess.CalledProcessError as error:
    print("programm returned non-zero exit status", file=sys.stderr)
    returncode = error.returncode
exit(returncode)  # You'll only reach this if an exception occurred.

That way you shouldn't get a traceback (though I actually can't reproduce getting the message you get, even if I leave the exit inside the except block).

edited Jul 23, 2014 at 19:37

answered Jul 23, 2014 at 19:29

dano

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3 Comments

Wilhelm Schuster Over a year ago

That way I don't get a During handling of the above exception, another exception occurred:, but I get a traceback nonetheless (from exit()), but I guess that's what exit() does - raising SystemExit.

dano Over a year ago

@WilhelmSchuster What environment are you executing this code in? I don't normally see a traceback for a call to exit or sys.exit.

Wilhelm Schuster Over a year ago

I was running it via python3 -i script.py (makes debugging easier). You're right, with python3 script.py no traceback is shown. Thanks.

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