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How to Exit a Python Program: sys.exit()

Posted: | Tags: Python

To exit a Python program before it completes, use sys.exit().

This article also covers the built-in functions exit() and quit() for ending a Python REPL (interactive mode) session, and shows how to forcefully stop a running program from the terminal or command prompt using the Ctrl + C shortcut—especially useful when a program becomes stuck in an infinite loop.

Contents

Exit a Python program: sys.exit()

Basic usage

When sys.exit() is called, the Python program terminates immediately.

Any lines of code following sys.exit() will not be executed.

import sys

print('Start')

sys.exit()

print('Finish')
source: sys_exit.py
$ python sys_exit.py
Start
source: sys_exit_sh.log

You can combine it with an if statement to make the program exit only under specific conditions.

import sys

a = 100

print('Start')

if a == 0:
    sys.exit()

print('Continue')

if a == 100:
    sys.exit()

print('Finish')
source: sys_exit_if.py
$ python sys_exit_if.py
Start
Continue
source: sys_exit_sh.log

Specify exit status or error messages

You can pass an argument to sys.exit() to specify the program’s exit status.

If no argument is passed, the exit status is 0, indicating a normal termination. To indicate an abnormal termination, pass a non-zero integer.

If a non-integer is passed, it is printed to standard error (stderr), and the exit status is set to 1. For example, passing a string allows you to display an error message.

import sys

sys.exit('Error message')
source: sys_exit_stderr.py
$ python sys_exit_stderr.py
Error message
source: sys_exit_sh.log

You can confirm that the message is output to stderr by redirecting stdout and stderr to separate files like this:

$ python sys_exit_stderr.py 1> data/temp/stdout.txt 2> data/temp/stderr.txt
source: sys_exit_sh.log

In this example, stdout.txt will be empty, while stderr.txt will contain Error message.

$ cat data/temp/stdout.txt

$ cat data/temp/stderr.txt
Error message
source: sys_exit_sh.log

In the example, the cat command displays the contents of a file on UNIX systems. On Windows, you would use type instead.

The SystemExit exception

sys.exit() raises a SystemExit exception.

If sys.exit() is called inside a try block, a bare except clause (without specifying the exception type) will catch the SystemExit exception, preventing the program from exiting.

import sys

print('Start')

try:
    sys.exit()
except:
    print('Catch all exceptions')

print('Finish')
source: sys_exit_systemexit.py
$ python sys_exit_systemexit.py
Start
Catch all exceptions
Finish
source: sys_exit_sh.log

To handle exceptions properly, always specify the expected exception type or use the base class Exception. For more on exception handling, see the article below:

Exit the REPL (interactive mode): exit(), quit()

To exit the Python REPL (interactive mode), you can use the built-in functions exit() and quit().

$ python 
Python 3.12.4 (main, Jun  6 2024, 18:26:44) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

Note that exit() and quit() are intended for use in the REPL only and should not be used in Python scripts (.py files).

Also, if you type exit or quit without parentheses, you'll see a message suggesting you can also use Ctrl + D to exit.

$ python
Python 3.12.4 (main, Jun  6 2024, 18:26:44) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit
Use exit() or Ctrl-D (i.e. EOF) to exit
>>> ^D

Forcefully terminate a running Python program: Ctrl + C

To forcefully stop a running Python program in the terminal or command prompt, use the keyboard shortcut Ctrl + C.

This is especially useful when your program gets stuck, for example, in an infinite loop.

Simply press Ctrl + C while the program is running, and it will terminate immediately.

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