Explaining the Difference between Exiting Functions with exit() and raise in Python

I’m writing a function deleting all JSON schemas on a server and I want an explicit confirmation that the user knows what he’s doing. I want to confirm his intentions. I’m wondering if using exit with a message/error code is a proper way (raise is better? ) + how to test this flow + how to differentiate between 2 exit statements at hand (exit() VS sys.exit())

Pavol Kutaj

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Jun 30, 2023

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Exiting a Python Function with exit VS raise <error>

• I am using sys.exit() which has a similar functionality to exit()

def confirm(intention: str) -> None:
    if intention != "yes I am serious":
        sys.exit("Confirmation failed. Exiting..."

• exit() or sys.exit() raise SystemExit exception.
• However, using raise to raise a proper exception instead of calling exit() would enable handling errors in a specific way, e.g.

def confirm(intention: str) -> None:
    if intention != "yes I am serious":
        raise ValueError("Confirmation failed")

• Elsewhere in the code, you may be catching the exception to allow handling it in a way that makes sense for the program (save a file before exiting, logging, etc..) and re-raising it to finally exit

On exit() VS sys.exit(): one for REPL another for programs

• Both raise the SystemExit exception.
• exit() is intended for use in the interactive shell.
• sys.exit() is intended for use in programs.
• sys.exit() is recommended for use in production code.

In pytest unit testing of sys.exit(), use pytest.raises() context manager with SystemExit exception type

import pytest
def test_confirm():
    intention = "no"
    with pytest.raises(SystemExit):
        confirm(intention)

    intention = ""
    with pytest.raises(SystemExit):
        confirm(intention)

    intention = "yes I am serious"
    confirm(intention)