Python how to exit main function

Question

Possible Duplicates:
Terminating a Python script
Terminating a Python Program

My question is how to exit out in Python main function? I have tried 'return' but it gave the error SyntaxError: 'return' outside function. Can anyone help? Thanks.

if __name__ == '__main__':
  try:
    if condition:
    (I want to exit here) 
    do something
  finally:
    do something

WHen you searched what did you find? http://stackoverflow.com/search?q=%5Bpython%5D+exit. All of these seem to have something in common. — S.Lott, Sep 28 '10 at 18:25
I think people have missed the point of this question. The OP is not looking for a generic way to terminate a program. He wants to know why, in this case, `return` does not work for that purpose. — Brent Bradburn, Apr 07 '12 at 16:00
This answer to a related question seems the most useful here http://stackoverflow.com/a/953385/86967. — Brent Bradburn, Apr 07 '12 at 16:01

score 124 · Accepted Answer · answered Sep 28 '10 at 18:21

124

You can use sys.exit() to exit from the middle of the main function.

However, I would recommend not doing any logic there. Instead, put everything in a function, and call that from __main__ - then you can use return as normal.

answered Sep 28 '10 at 18:21

Daniel Roseman

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+1 for adding an explicit 'everything' function. This also makes it easier to (1) call this script from other scripts (2) unit test. – Manoj Govindan Sep 28 '10 at 18:23
8

Guido van Rossum supports (or at least, used to) this approach: http://www.artima.com/weblogs/viewpost.jsp?thread=4829 – ide Sep 28 '10 at 18:23
1

I typically create a function named "main" and put it at the top of the file. – Bryan Oakley Sep 28 '10 at 18:36
exit() works fine for me, using python 2.7.x – radtek May 02 '14 at 19:25

score 36 · Answer 2 · answered Sep 28 '10 at 18:21

36

You can't return because you're not in a function. You can exit though.

import sys
sys.exit(0)

0 (the default) means success, non-zero means failure.

answered Sep 28 '10 at 18:21

Matthew Flaschen

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Why `sys.exit()` instead of just plain `exit()`? – Kirk Strauser Sep 28 '10 at 18:26
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Why not? Also, Python tries not to provide more built-in functions than are necessary. – David Z Sep 28 '10 at 18:32
3

@Just, the [docs](http://docs.python.org/library/constants.html#exit) say not to use plain `exit` in programs, and it's arguably a [bug](http://bugs.python.org/issue8220) (albeit a WONTFIX) that you even can. – Matthew Flaschen Sep 28 '10 at 18:42
The exit() is defined in site.py and it works only if the site module is imported so it should be used in the interpreter only. https://www.scaler.com/topics/exit-in-python/ https://www.geeksforgeeks.org/python-exit-commands-quit-exit-sys-exit-and-os-_exit/ – bgrupczy May 16 '23 at 01:12

score 13 · Answer 3 · answered Sep 28 '10 at 18:34

13

If you don't feel like importing anything, you can try:

raise SystemExit, 0

answered Sep 28 '10 at 18:34

ecik

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Can this be caught if someone wanted to extend the main and not exit at the end of it? – ThorSummoner Aug 21 '15 at 17:54

score 7 · Answer 4 · answered Sep 28 '10 at 18:20

7

use sys module

import sys
sys.exit()

answered Sep 28 '10 at 18:20

pyfunc

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score 2 · Answer 5 · answered Sep 28 '10 at 18:20

2

Call sys.exit.

answered Sep 28 '10 at 18:20

SLaks

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Python how to exit main function

5 Answers5