What are decorators in python

 

(13)DECORATORS:

A decorator is a function that takes another function as an argument that extends the behavior of this function without explicitly modifying it.

It allows you to add new functionality to an existing function. There are two types of decorators class decorators and function decorators first function decorator.

1.Function decorator:

for example: 

def start_end_decorator(func):

    

    def wrapper():

        print('Start')

        func()

        print('End')

    return wrapper

def print_name():

    print('Alex')

    

print_name()

print()

# Now wrap the function by passing it as argument to the decorator function

# and asign it to itself -> Our function has extended behaviour!

print_name = start_end_decorator(print_name)

print_name()

output = 

Alex

Start

Alex

End

To print sum with help of the decorators.

for example:

def start_end_decorator_3(func):

    def wrapper(*args, **kwargs):

        print('Start')

        result = func(*args, **kwargs)

        print('End')

        return result

    return wrapper

@start_end_decorator_3

def add_5(x):

    return x + 5

result = add_5(10)

print(result)

output = 

Start

End

15

 

To identify the function.

for example:

def start_end_decorator_3(func):

    def wrapper(*args, **kwargs):

        print('Start')

        result = func(*args, **kwargs)

        print('End')

        return result

    return wrapper

@start_end_decorator_3

def add5(x):

    return x + 5

print(help(add5))

print(add5.__name__)

output = Help on function wrapper in module __main__:

wrapper(*args, **kwargs)

None

wrapper

To print a sentence multiple times.

for example:

import functools

def my_decorator(func):

    @functools.wraps(func)

    def wrapper(*args, **kwargs):

        # Do something before

        result = func(*args, **kwargs)

        # Do something after

        return result

    return wrapper

def repeat(num_times):

    def decorator_repeat(func):

        @functools.wraps(func)

        def wrapper(*args, **kwargs):

            for _ in range(num_times):

                result = func(*args, **kwargs)

            return result

        return wrapper

    return decorator_repeat

@repeat(num_times=3)

def greet(name):

    print(f"Hello {name}")

    

greet('Alex')

output = 

Hello Alex

Hello Alex

Hello Alex

2.Class decorator:

for exmple:

import functools

class CountCalls:

    def __init__(self, func):

        functools.update_wrapper(self, func)

        self.func = func

        self.num_calls = 0

    # extend functionality, execute function, and return the result

    def __call__(self, *args, **kwargs):

        self.num_calls += 1

        print(f"Call {self.num_calls} of {self.func.__name__!r}")

        return self.func(*args, **kwargs)

@CountCalls

def say_hello(num):

    print("Hello!")

say_hello(5)

say_hello(5)

output = 

Call 1 of 'say_hello'

Hello!

Call 2 of 'say_hello'

Hello!