What are decorators and how to use them in Python

In Python, a decorator is a function that takes another function as an argument and returns a new function that generally extends the behavior of the original.

Decorators allow modifying or extending the behavior of functions or methods without changing their source code. They are widely used for cross-cutting concerns such as authentication, logging, and validation, among others.

Defining a Decorator

Let’s see it with an example

def my_decorator(func):
    def wrapper():
        print("Something is done before the function")
        func()
        print("Something is done after the function")
    return wrapper

Using a Decorator

Now, to use the decorator the @ symbol followed by the decorator’s name is used, before the definition of the function to be decorated.

@my_decorator
def greet():
    print("Hello from LuisLlamas.es!")

greet()

# Output:
# Something is done before the function
# Hello from LuisLlamas.es!
# Something is done after the function

Decorators with Arguments

Decorators can also accept arguments. To do this, functions need to be nested:

• An outer function to accept the decorator’s arguments
• An inner function that accepts the function to be decorated.

For example,

def repeat(n):
    def decorator(func):
        def wrapper(*args, **kwargs):
            for _ in range(n):
                func(*args, **kwargs)
        return wrapper
    return decorator

@repeat(3)
def say_goodbye():
    print("Goodbye!")

say_goodbye()

# Output:
# Goodbye!
# Goodbye!
# Goodbye!

Multi-level Decorators

Python allows nesting decorators, applying multiple decorators to the same function.

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

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

@decorator1
@decorator2
def function():
    print("Function is running")

function()

# Output:
# Decorator 1 before
# Decorator 2 before
# Function is running
# Decorator 2 after
# Decorator 1 after