# What is decorators in python

Decorators are used to add functionalities to an object without changing the structure of the object

## Let's see how a function looks like

def add_one(no):
    return no + 1

num = add_one
num(5)

> Output: 6

## Let's see an example of Inner/nested function 🤔

def add_one(no):
    def add_two(no):
        return no + 2

    return add_two(no)
	
print(add_one(4))

> Output: 6

## Let's see what will happen if we pass function as a parameter to a different function

def add_one(number):
    return number + 1

def fun(function):
    to_add = 5
    return function(to_add)

print(fun(add_one))

> Output: 6

we have created two function where `fun` can have function as parameter and we are passing `add_one` as a function parameter to `fun` function

then we are passing the `to_add` value to the `add_one`
function

Now you're getting, how we are going to get to decorators.

## We can also return functions from functions

def parent(num):
	def first_child():
		return "It's Itachi"
		
	def second_child():
		return "I'm Sasuke"	
	if num == 1:
		print(first_child())
		return first_child
	else:
		print(second_child())
		return second_child

first = parent(1)
second = parent(2)

print(first)
print(second)

> It's Itachi
> I'm Sasuke
> <function parent.<locals>.first_child at 0x7f6e5c7ff820>
> <function parent.<locals>.second_child at 0x7f6e5c7ff940>

first()
#>>> It's Itachi
second()
#>>> I'm Sasuke

Note: we are returning `first_child` without parentheses. this means we are returning a reference to the function `first_child`. Where `first_child()` with parentheses returns the result of the function.

Python also allows to use functions as return values.

> ### **This is why functions are called First-Class Objects**

functions can be passed around and used as arguments, just like any other object (str, int, bool, list, etc).

## What is `Closure`
not closer from chainsmokers 😅

def print_message(message):
    "Outer Function"
    def send_message():
        "Nested Function"
        print(message)

    send_message()

print_message("Some message")

> Output: Some message

# @Decorators

First using normal function

def uppercase_decorator(function):
    def wrapper():
        func = function()
        make_uppercase = func.upper()
        return make_uppercase

    return wrapper
    
def hello():
    return "Hey there"
    
decorate = uppercase_decorator(hello)
print(decorate())

> Output: HEY THERE

Now same thing using decorator

def uppercase_decorator(function):
    def wrapper():
        func = function()
        make_uppercase = func.upper()
        return make_uppercase

    return wrapper
    

@uppercase_decorator
def hello():
    return "using decorator"

print(hello())

> Output: USING DECORATOR

To debug decorators we can use functools

import functools

def uppercase_decorator(func):
    @functools.wraps(func)
    def wrapper():
        return func().upper()
    return wrapper
@uppercase_decorator
def say_hi():
    "This will say hi"
    return 'hello there'

print(say_hi())
print(say_hi.__name__)
print(say_hi.__doc__)

> Output: HELLO THERE
> say_hi
> This will say hi

###### tags: `python` `decorators` `interview`