How do I exit Python if run from command line, otherwise print stack trace

Question

I want to exit Python if I encounter an exception in my function if that function is being executed from the command line, but want to raise an exception and print a stack trace if the my function is not run from the command line.

Right now I have

    try:
        #...
    except Exception as e:
        print('ERROR: Some useful message')
        if __name__ == '__main__':
            raise SystemExit
        else:
            raise e

but I feel like I'm either doing too much here, or too little.

Is there an idiomatic way to get a stack trace with the original exception when my function is run from the command line; but simply exit if it is being run from the command line?

could you rephrase this Is there an idiomatic way to get a stack trace with the original exception when my function is run from the command line; but simply exit if it is being run from the command line?. I'm not sure if that makes. thanks. — Haleemur Ali
– Haleemur Ali, Commented Feb 27, 2015 at 15:18
Are you trying to prevent your end users from seeing a traceback? If so, I'm not sure I agree with the wisdom of this strategy. Tracebacks contain useful information for you, the programmer. If the end user can just copy and paste the traceback, it can save you a fair amount of debugging time. — Kevin
– Kevin, Commented Feb 27, 2015 at 15:21
@Kevin: It's not that kind of error. Here try is just a test for something. When used from the command line in the context of a isolated command, it could fail without downstream consequences. But if the function has been imported and used, the user importing probably needs to decide for himself whether to exit, so I show the stack trace. — orome
– orome, Commented Feb 27, 2015 at 15:26

Antti Haapala · Accepted Answer · 2015-02-27 15:21:18Z

4

The better way would be to do this:

import sys

def func():
    do_actual_processing()
    if not successful:
        raise Exception("Yadayada")

if __name__ == '__main__'
    try:
        func()
    except Exception as e:
        sys.exit(1)

That is, the function itself does not need to be concerned with whether or not it is run from command line.

answered Feb 27, 2015 at 15:21

Antti Haapala

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6 Comments

orome Over a year ago

Oh wait, I know why: I don't want to do this for all exceptions, or even for all exceptions of a give class. Just for certain exceptions in certain places in the code. E.g., I could have another exception happen somewhere else in my code and not want to exit, ever.

Antti Haapala Over a year ago

Sounds like bad design. I would do a main function then for command line usage, it really is not a good idea to make a function do something completely different just because __name__ == '__main__'

orome Over a year ago

I think you're looking at this the wrong way (or maybe I'm asking the wrong question): If this is executed from the command line I want to print a message of my own and exit; but if it's not, I want the stack trace and the original exception.

orome Over a year ago

The context is that each of these functions (there are several) corresponds to a command for a script (e.g. myscript.py func). I don't want a full stack trace if that fails; but to just exit with a simple message like "Something I need to proceed isn't here". But if func has been imported and is being used, say, in IPython, I want to be more informative, with the full trace and original exception.

Antti Haapala Over a year ago

Then why not do as I said, this hardly invalidates my answer.

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