Hyppää sisältöön

Ei vielä käännetty

Tätä sivua ei ole vielä käännetty suomeksi, joten se näytetään englanniksi. Auta kääntämään

exit() and quit() Functions

The exit() and quit() functions terminate the Python interpreter. Typically used in interactive mode.

Complexity Reference

Operation Time Space Notes
exit() O(1) O(1) Terminate immediately
quit() O(1) O(1) Terminate immediately

Basic Usage

Exit from Interactive Mode

# In Python REPL:
>>> exit()
# Interpreter terminates

# Or:
>>> quit()
# Interpreter terminates

# Can also use Ctrl+D on Unix/Mac or Ctrl+Z+Enter on Windows

Using sys.exit() in Scripts

import sys

def main():
    if not valid_input():
        sys.exit(1)  # Exit with error code

    process_data()
    sys.exit(0)  # Exit successfully

if __name__ == "__main__":
    main()

Exit Codes

Exit Code Meanings

import sys

# Exit codes convention:
# 0 = success
# non-zero = error

sys.exit(0)   # Success
sys.exit(1)   # General error
sys.exit(2)   # Misuse of shell command
sys.exit(126) # Command invoked cannot execute
sys.exit(127) # Command not found

Checking Exit Code

# In shell:
$ python script.py
$ echo $?  # Prints exit code
# 0

Difference Between exit() and quit()

exit() vs quit()

# Both behave identically in interactive mode
# In scripts, neither should be used - use sys.exit() instead

# ✅ DO: Use sys.exit() in scripts
import sys
sys.exit(0)

# ❌ DON'T: Use exit() or quit() in scripts
exit()  # May not work if site module not loaded
quit()  # May not work if site module not loaded

In Scripts vs Interactive

# REPL (interactive):
>>> exit
# <site._Printers.Quitter object at 0x...>

>>> exit()
# Quits interpreter

# Script (non-interactive):
# exit and quit are only available via site module
# Use sys.exit() instead

Practical Examples

Conditional Exit

import sys

def validate_config(config_file):
    try:
        with open(config_file) as f:
            return json.load(f)
    except FileNotFoundError:
        print(f"Error: {config_file} not found")
        sys.exit(1)
    except json.JSONDecodeError:
        print(f"Error: {config_file} is not valid JSON")
        sys.exit(1)

if __name__ == "__main__":
    config = validate_config("config.json")
    process(config)
    sys.exit(0)

Exit with Message

import sys

def process_data(filename):
    if not filename:
        print("Error: Filename required")
        sys.exit(2)

    if not os.path.exists(filename):
        print(f"Error: File not found: {filename}")
        sys.exit(1)

    # Process file
    with open(filename) as f:
        data = f.read()

    return data

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: script.py <filename>")
        sys.exit(2)

    data = process_data(sys.argv[1])
    print(data)
    sys.exit(0)

Exit in Exception Handler

import sys
import logging

logging.basicConfig(level=logging.INFO)

try:
    result = risky_operation()
except Exception as e:
    logging.error(f"Operation failed: {e}")
    sys.exit(1)
else:
    logging.info("Operation succeeded")
    sys.exit(0)
finally:
    cleanup()

Cleanup with finally

Ensure Cleanup Runs

import sys

def main():
    resource = acquire_resource()

    try:
        process(resource)
    except Exception as e:
        print(f"Error: {e}")
        sys.exit(1)
    finally:
        # This ALWAYS runs, even with sys.exit()
        cleanup(resource)

if __name__ == "__main__":
    main()

Using atexit Module

import sys
import atexit

def cleanup():
    print("Cleaning up...")
    # Cleanup code

# Register cleanup to run before exit
atexit.register(cleanup)

# Now cleanup() will run on any exit
sys.exit(0)

Exit Status Conventions

Standard Exit Codes

import sys

# 0: Success
# 1: General errors
# 2: Misuse of shell builtin
# 126: Command cannot execute
# 127: Command not found
# 128+N: Fatal signal N
# 130: Script terminated by Ctrl+C (128 + 2)

def main():
    if validation_failed():
        sys.exit(1)  # General error

    if permission_denied():
        sys.exit(13)  # Permission denied

    if file_not_found():
        sys.exit(2)   # Misuse/not found

    sys.exit(0)  # Success

if __name__ == "__main__":
    main()

Testing Exit Behavior

Using pytest

import pytest
import sys

def application_exit():
    sys.exit(42)

def test_exit_code():
    with pytest.raises(SystemExit) as exc_info:
        application_exit()

    assert exc_info.value.code == 42

Using unittest

import unittest
import sys

class TestExit(unittest.TestCase):
    def test_exit_code(self):
        with self.assertRaises(SystemExit) as cm:
            sys.exit(5)

        self.assertEqual(cm.exception.code, 5)

Best Practices

import sys

# ✅ DO: Use sys.exit() in scripts
import sys
sys.exit(0)

# ✅ DO: Use meaningful exit codes
sys.exit(1)  # Error

# ✅ DO: Print error message before exit
print("Error: something failed", file=sys.stderr)
sys.exit(1)

# ✅ DO: Use finally for cleanup
try:
    code()
finally:
    cleanup()

# ❌ DON'T: Use exit() in scripts
exit()  # May not work

# ❌ DON'T: Use exit() in libraries
# Libraries should raise exceptions, not exit

# ❌ DON'T: Exit silently
sys.exit(0)  # Should print why before exiting