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ICSM Computer

ICSM Computer

02-Jun-2025

Decorators in Python are a powerful and elegant way to modify or enhance the behavior of functions or methods without changing their actual code.

What is a decorator?

  • A decorator is essentially a function that takes another function as input and returns a new function that adds some kind of functionality before or after the original function runs.
  • You apply decorators using the @decorator_name syntax placed just above the function definition.

Why use decorators?

  • To add reusable functionality (e.g., logging, timing, access control) to many functions without repeating code.
  • To keep your code clean and separate concerns.

Basic example of a decorator

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

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

say_hello()

Output:

Before the function runs
Hello!
After the function runs

How it works:

@my_decorator is syntactic sugar for:

say_hello = my_decorator(say_hello)

When you call say_hello(), it actually calls wrapper(), which runs extra code around the original function.

Decorators with arguments

To decorate functions that take parameters, your wrapper function should accept *args and **kwargs:

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

@decorator
def greet(name):
    print(f"Hello, {name}!")

greet("Alice")

Summary

  • Decorators wrap a function to extend its behavior.
  • They’re commonly used for logging, memoization, access control, performance measurement, etc.
  • Python includes built-in decorators like @staticmethod, @classmethod, and @property.
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