Decorator in Python

 

Decorator in Python

A decorator in Python is a function that modifies the behavior of another function — without changing its actual code.

You can think of decorators as wrappers around functions: they let you add extra functionality before or after a function runs.

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📌 Why Use Decorators?

• Logging

• Timing function execution

• Access control

• Code reuse

• Input validation

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✅ Basic Syntax

@decorator_name
def some_function():
    # code

✅ Simple Example of a Decorator

🔹 Step 1: Define a Decorator Function

def my_decorator(func):
    def wrapper():
        print("Before the function runs")
        func()
        print("After the function runs")
    return wrapper

🔹 Step 2: Apply the Decorator

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

say_hello()

Output:

Before the function runs
Hello!
After the function runs

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✅ Example with Arguments

def debug_decorator(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with arguments {args}")
        result = func(*args, **kwargs)
        print(f"{func.__name__} returned {result}")
        return result
    return wrapper

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

add(3, 4)

Output:

Calling add with arguments (3, 4)
add returned 7

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✅ Real-Life Use: Timing a Function

import time

def timer_decorator(func):
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} took {end - start:.4f} seconds")
        return result
    return wrapper

@timer_decorator
def long_running_task():
    time.sleep(2)
    print("Task complete")

long_running_task()

Output
Task complete
long_running_task took 2.0014 seconds

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✅ Summary

Term	Meaning
@decorator_name	Syntax to apply a decorator
wrapper()	Inner function that adds extra code
*args, **kwargs	To allow any number of arguments