Introduction to Decorators in Python

Decorators allow you to modify or enhance functions without changing their actual code. They are a powerful feature in Python.

1) Functions as First-Class Citizens

In Python, functions are first-class objects. This means you can:

Assign a function to a variable
Pass a function as an argument to another function
Return a function from another function
Store functions in lists, dictionaries, etc.


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

say_hello = greet  # Assign function to a variable
say_hello()        # Output: Hello!

def call_func(f):
    f()

call_func(greet)   # Output: Hello!

def outer():
    def inner():
        print("Inside inner function")
    return inner

my_func = outer()
my_func()          # Output: Inside inner function

All of these concepts are what make decorators possible!

2) What is a Decorator?

A decorator is a function that:

Takes another function as an argument
Wraps or modifies its behavior
Returns a new function

Think of it as a “wrapper” around a function that adds extra functionality.

3) Simple Decorator Example


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

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

decorated = decorator_func(say_hello)
decorated()
# Output:
# Before the function runs
# Hello!
# After the function runs

Here, decorator_func takes say_hello and returns a modified version.

4) Using `@` Syntax


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

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

say_hello()
# Output:
# Before the function runs
# Hello!
# After the function runs

The @decorator_func is just shorthand for say_hello = decorator_func(say_hello).

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Monday, August 25, 2025