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AtExit (atexit) Module

The atexit module in Python allows you to register functions that will run automatically when the program is about to exit.

  • This is useful for performing cleanup tasks like closing files, releasing resources, or printing goodbye messages.

Basic Usage of atexit

  • Registering Functions: Use atexit.register(function_name) to register a function that will be called upon program termination.

  • Automatic Execution: Registered functions are executed in the reverse order of their registration when the program exits normally (no crashes or os._exit).

  • Unregistering Functions: You can unregister a function using atexit.unregister(function_name).

Registering a Function

import atexit

def goodbye():
    print("Program is exiting... Goodbye!")

# Register the function
atexit.register(goodbye)

# Program logic
print("Hello, World!")

Output:

Hello, World!
Program is exiting... Goodbye!

Multiple Registered Functions

import atexit

def func1():
    print("First cleanup function.")

def func2():
    print("Second cleanup function.")

# Register both functions
atexit.register(func1)
atexit.register(func2)

print("Program is running...")

Output:

Program is running...
Second cleanup function.
First cleanup function.

Note: Functions are called in reverse order of their registration (func2 runs before func1).

Passing Arguments to Functions

You can use atexit.register with additional arguments:

import atexit

def greet(name):
    print(f"Goodbye, {name}!")

# Register with arguments
atexit.register(greet, "Alice")

print("Program is running...")

Output:

Program is running...
Goodbye, Alice!

Using lambda Functions

You can register anonymous functions with lambda:

import atexit

atexit.register(lambda: print("Lambda function executed!"))

print("Program is running...")

Output:

Program is running...
Lambda function executed!

atexit decorator

import atexit

@atexit.register
def goodbye():
    print('You are now leaving the Python sector.')

Key Points to Remember

  1. Normal Exit Only: Functions registered with atexit are executed only during a normal exit (not if the program crashes or os._exit() is called).

  2. Reverse Execution: Functions are executed in reverse order of their registration.

  3. Use Cases: Cleanup tasks, logging program termination, closing open resources.

Summary

  • The atexit module is a handy way to manage cleanup tasks when your program exits.
  • By registering functions with atexit.register, you ensure they run automatically at termination.
  • It’s particularly useful for tasks like saving state, closing connections, or releasing resources.