Concepts - Decorators in Python

Hope you have understood from the previous course Functions and OOPs, what is a function? Now, let us understand what is a higher order function.

A Higher Order function is a function, which is capable of doing any one of the following things:

It can be functioned as a data and be assigned to a variable.

It can accept any other function as an argument.

It can return a function as its result.

The ability to build Higher order functions, allows a programmer to create Closures, which in turn are used to create Decorators.

Decorators are evolved from the concept of closures.

A decorator function is a higher order function that takes a function as an argument and returns the inner function.
A decorator is capable of adding extra functionality to an existing function, without altering it.

Examples

Without decorator

def outer(x, y):
    def inner1():
        return x + y

    def inner2():
        return x * y

    return inner1, inner2


f1, f2 = outer(10, 25)

print(f1()) # 35
print(f2()) # 250

def outer(x, y):
    def inner1():
        return x + y

    def inner2(z):
        return inner1() + z

    return inner2


f = outer(10, 25)

print(f(15)) # 10 + 25 + 15 = 50 (result)

Problem while using decorator is the function name

def outer(func):
    def inner():
        print("Accessing: ", func.__name__)
        return func()

    inner.__name__ = func.__name__
    return inner


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


print(greet.__name__) # greet

Using from functools import wraps for Function Name ref - Stack Overflow

from functools import wraps


def decorator_func(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)

    return wrapper


@decorator_func
def square(x):
    return x ** 2


print(square.__name__) # square

def bind(func):
    func.data = 9
    return func


@bind
def add(x, y):
    return x + y


print(add(3, 10)) # 13
print(add.data)  # 9

Example - 1


from functools import wraps


def star_print(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        print(5 * "*")
        func(*args, **kwargs)
        print(5 * "*")

    return wrapper


def hash_print(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        print(5 * "#")
        func(*args, **kwargs)
        print(5 * "#")

    return wrapper


@star_print
@hash_print
def greet(msg):
    print(msg)


greet('hello')
print(greet.__name__)

Output

*****
#####
hello
#####
*****
greet

Example - 2

Function Input Data validation with decorators

from functools import wraps


def smart_divide(func):
    @wraps(func)
    def wrapper(*args):
        a, b = args
        if b == 0:
            print('oops! cannot divide')
            return
        return func(*args)

    return wrapper


@smart_divide
def divide(a, b):
    return a / b


print(divide.__name__)
print(divide(4, 16))
print(divide(8, 0))
print(divide(8, 1))

Output

divide
0.25
oops! cannot divide
None
8.0