Python Decorators

A Decorator is a function that modifies or extends the behavior of another function without changing its original code.

Decorators are commonly used for logging, authentication, validation, and performance monitoring.

Basic Function Example

Example

def greet():
    print("Hello")

greet()

Output:

Hello

Creating a Decorator

Example

def my_decorator(func):
    def wrapper():
        print("Before Function")
        func()
        print("After Function")
    return wrapper

def greet():
    print("Hello")

greet = my_decorator(greet)

greet()

Output:

Before Function
Hello
After Function

Using @ Decorator Syntax

Python provides the @ symbol as a shortcut for applying decorators.

Example

def my_decorator(func):
    def wrapper():
        print("Before Function")
        func()
        print("After Function")
    return wrapper

@my_decorator
def greet():
    print("Hello")

greet()

Output:

Before Function
Hello
After Function

Decorator with Arguments

Example

def my_decorator(func):
    def wrapper(name):
        print("Welcome")
        func(name)
    return wrapper

@my_decorator
def greet(name):
    print("Hello", name)

greet("John")

Output:

Welcome
Hello John

Returning Values from Decorators

Example

def my_decorator(func):
    def wrapper():
        return func() * 2
    return wrapper

@my_decorator
def get_number():
    return 10

print(get_number())

Output:

20

Multiple Decorators

Example

def decorator1(func):
    def wrapper():
        print("Decorator 1")
        func()
    return wrapper

def decorator2(func):
    def wrapper():
        print("Decorator 2")
        func()
    return wrapper

@decorator1
@decorator2
def greet():
    print("Hello")

greet()

Output:

Decorator 1
Decorator 2
Hello

Real-World Example

Example

def login_required(func):
    def wrapper():
        print("Checking Login...")
        func()
    return wrapper

@login_required
def dashboard():
    print("Dashboard Opened")

dashboard()

Output:

Checking Login...
Dashboard Opened

Summary

• Decorators modify the behavior of functions.
• A decorator is a function that accepts another function.
• The @ syntax is used to apply decorators.
• Decorators help avoid code duplication.
• They are commonly used for logging, authentication, caching, and validation.
• Multiple decorators can be applied to a single function.