Decorators in Python

We will discuss about the decorators in Python in this blog. A decorator is a function that takes another function as an argument, and it returns a function with enhanced functionality.
You might have seen @staticmethod, @classmethod, and @property in your Python project code, all are example of decorators.

We will discuss first requirements and then will discuss @staticmethod, @classmethod, and @property decorators with example and code.
The things that we should know before decorators
Everything in Python is an object:
 


def book(name="Atomic Habits"):
    return f"self-help book: {name}"

print(book())
# Output: self-help book: Atomic Habits

book_description = book

print(book_description())
# Output: self-help book: Atomic Habits


Defining functions within functions: 


def book(name="Atomic Habits"):
    print("You are in the book() function")

    def self_help_book():
        return f"You are in the self_help_book() function."

    def algorithm_book():
        return f"You are in the algorithm_book() function."

    print(self_help_book())
    print(algorithm_book())
    print("You are in the book() function")

book()

# Output: You are in the book() function
# You are in the self_help_book() function.
# You are in the algorithm_book() function.
# You are in the book() function



Returning functions from within functions:

def book(name="Atomic Habits"):
    print (f"{name} books is a really good book")

    def book_zoner():
        return (f"{name}: is a self help book.")

    return book_zoner

a = book()
print(a)
# Output: Atomic Habits books is a really good book
# .book_zoner at 0x105044400>



Giving a function as an argument to another function

def book():
    print("Atomic Habits is a very good book.")


def gener_of_book(function):
    print("Atomic habits book is self help book")
    function()
    print("After calling argument passed function")

gener_of_book(book)
# Output
# Atomic habits book is self help book
# Atomic Habits is a very good book.
# After calling argument passed function


Above logic is used in a decorator. The decorator adds or modifies the functionality of the existing.

Writing your first decorator

def make_new_decorator(function):

    def wrapTheFunction():
        print("I am doing great work in the field of AI")

        function()

        print("I am doing great work in the field of AI")


    return wrapTheFunction

def book_review():
    print("Cracking the coding interview Book by Gayle Laakmann McDowell is very good book for DSA")

book_review()
# Outputs: "Cracking the coding interview Book by Gayle Laakmann McDowell is very good book for DSA"

a_function_requiring_decoration = make_new_decorator(book_review)
# now a_function_requiring_decoration is wrapped by wrapTheFunction()

a_function_requiring_decoration()
# Outputs: I am doing great work in the field of AI
# Cracking the coding interview Book by Gayle Laakmann McDowell is very good book for DSA
# I am doing great work in the field of AI



def make_new_decorator(function):

    def wrapTheFunction():
        print("I am doing the greate work in the field of AI")

        function()

        print("I am doing the greate work in the field of AI")


    return wrapTheFunction

@make_new_decorator
def book_review():
    print("Cracking the coding interview Book by Gayle Laakmann McDowell is very good book for DSA")

book_review()
# Outputs: I am doing the greate work in the field of AI
# Cracking the coding interview Book by Gayle Laakmann McDowell is very good book for DSA
# I am doing the greate work in the field of AI


Syntax of Decorator Parameters


def decorator_name(func):
    def wrapper(*args, **kwargs):
        # Add functionality before the original function call
        result = func(*args, **kwargs)
        # Add functionality after the original function call
        return result
    return wrapper


@decorator_name
def function_to_decorate():
    # Original function code
    pass



Common Built-in Decorators in Python
1. @staticmethod
2. @classmethod
3. @property

@staticmethod
staticmethod decorator is used to define a method that does not operate in the instance of the class. It is called by the class itself, not by the instance of the class


class RecatangleArea:

    def __init_(self, height, width):
        self.height = height
        self.width = width

    def calculate_area_1(self):
        area = self.height*self.width
        return area

    @staticmethod
    def calculate_area_2(height, width):
        area = height*width
        return area

area = RecatangleArea.calculate_area_2(5,4)
print(area)

# You will get error when you run RecatangleArea.calculate_area_1(5,4) because calculate_area_1 require class instance
area = RecatangleArea.calculate_area_1(5,4)
print(area)


@classmethod


class RealState:
    property_price = 2 # price in crore

    @classmethod
    def price_of_new_house(cls, price):
        cls.property_price = price
        return cls.property_price

print(RealState.property_price)
# Output: 2
RealState.price_of_new_house(5)
print(RealState.property_price)
# Output: 5

real_state_object = RealState()
print(real_state_object.property_price)
# Output: 5


@property


class RecatangleArea:

    def __init__(self, h, w):
        self.rectanle_height = h
        self.rectanle_width = w

    @property
    def height(self):
        return self.rectanle_height

    @height.setter
    def height(self, h):
        self.rectanle_height = h

    @property
    def width(self):
        return self.rectanle_width

    @width.setter
    def width(self, w):
        self.rectanle_width = w

    def area(self):
        return self.rectanle_height*self.rectanle_width
    
area_object = RecatangleArea(5,4)
print(f"Height: {area_object.height}")
print(f"Width: {area_object.width}")
print(f"Area of the rectangle: {area_object.area()}")
# Output:
# Height: 5
# Width: 4
# Area of the rectangle: 20


area_object.height = 10
area_object.width = 8

print(f"Height: {area_object.height}")
print(f"Width: {area_object.width}")
print(f"Area of the rectangle: {area_object.area()}")
# Output:
# Height: 10
# Width: 8
# Area of the rectangle: 80



Sources
1. Python Bultin decorators List
2. Decorators in Python
3. Decorators