Explain the Python Decorators

ICSM 393 25-Sep-2025

A decorator in Python is a function that takes another function as input, adds some extra behavior, and returns a new function — without changing the original function’s code.

It’s often used for logging, authentication, caching, timing, etc.

How Functions Work in Python

In Python, functions are first-class objects — meaning you can:

Assign them to variables
Pass them as arguments
Return them from other functions
That’s why decorators are possible.

Basic Example (function inside function)

def outer_function(func):
    def inner_function():
        print("Before the function runs")
        func()
        print("After the function runs")
    return inner_function

def say_hello():
    print("Hello!")

# Wrap manually
decorated = outer_function(say_hello)
decorated()

Output:

Before the function runs
Hello!
After the function runs

Using `@decorator` Syntax

Python provides a shorthand with @:

def outer_function(func):
    def inner_function():
        print("Before")
        func()
        print("After")
    return inner_function

@outer_function   # same as: say_hi = outer_function(say_hi)
def say_hi():
    print("Hi there!")

say_hi()

Output:

Before
Hi there!
After

Decorator with Arguments

def my_decorator(func):
    def wrapper(*args, **kwargs):
        print("Before function")
        result = func(*args, **kwargs)
        print("After function")
        return result
    return wrapper

@my_decorator
def add(a, b):
    return a + b

print(add(5, 3))

Output:

Before function
After function
8

Real-World Examples

1. Logging

def log(func):
    def wrapper(*args, **kwargs):
        print(f"Running {func.__name__} with {args}, {kwargs}")
        return func(*args, **kwargs)
    return wrapper

@log
def multiply(a, b):
    return a * b

print(multiply(4, 5))

2. Authentication Example

def require_admin(func):
    def wrapper(user, *args, **kwargs):
        if user != "admin":
            print("Access denied!")
            return
        return func(user, *args, **kwargs)
    return wrapper

@require_admin
def delete_user(user, target):
    print(f"{user} deleted {target}")

delete_user("guest", "Bob")   # denied
delete_user("admin", "Bob")   # allowed

Decorators for Classes

Python has built-in decorators too:

@staticmethod
@classmethod
@property

Example:

class Person:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name.upper()

p = Person("alice")
print(p.name)  # ALICE

A decorator is just a function that wraps another function.
Use @decorator_name above a function to apply it.
Very handy for cross-cutting concerns (logging, security, retry logic, etc.).

interview

Explain the Python Decorators

ICSM

Can you answer this question?

1 Answers

How Functions Work in Python

Basic Example (function inside function)

Using `@decorator` Syntax

Decorator with Arguments

Real-World Examples

1. Logging

2. Authentication Example

Decorators for Classes

Liked By

interview

Explain the Python Decorators

ICSM

Can you answer this question?

1 Answers

How Functions Work in Python

Basic Example (function inside function)

Using @decorator Syntax

Decorator with Arguments

Real-World Examples

1. Logging

2. Authentication Example

Decorators for Classes

Liked By

Using `@decorator` Syntax