Function Wrappers in Python

Wrappers around the functions are also knows as decorators which are a very powerful and useful tool in Python since it allows programmers to modify the behavior of function or class. Decorators allow us to wrap another function in order to extend the behavior of the wrapped function, without permanently modifying it. In Decorators, functions are taken as the argument into another function and then called inside the wrapper function.

Syntax:

@wrapper
def function(n):
    statements(s)

This is also similar to

def function(n):
    statement(s)

function = wrapper(function)

Let’s see the below examples for better understanding.
Example 1:

# defining a decorator
def hello_decorator(func):

    # inner1 is a Wrapper function in
    # which the argument is called

    # inner function can access the outer local
    # functions like in this case "func"
    def inner1():
        print("Hello, this is before function execution")

        # calling the actual function now
        # inside the wrapper function.
        func()

        print("This is after function execution")

    return inner1


# defining a function, to be called inside wrapper
def function_to_be_used():
    print("This is inside the function !!")


# passing 'function_to_be_used' inside the
# decorator to control its behavior
function_to_be_used = hello_decorator(function_to_be_used)


# calling the function
function_to_be_used()

Output:

Hello, this is before function execution
This is inside the function !!
This is after function execution

Example 2: Let’s define a decorator that count the time taken by the function for execution.

import time


def timeis(func):
    '''Decorator that reports the execution time.'''

    def wrap(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()

        print(func.__name__, end-start)
        return result
    return wrap

@timeis
def countdown(n):
    '''Counts down'''
    while n > 0:
        n -= 1

countdown(5)
countdown(1000)

Output:

countdown 1.6689300537109375e-06
countdown 5.507469177246094e-05

It’s critical to emphasize that decorators generally do not alter the calling signature or return value of function being wrapped. The use of *args and**kwargs is there to make sure that any input arguments can be accepted. The return value of a decorator is almost always the result of calling func(*args, **kwargs), where func is the original unwrapped function.

Please refer Decorators in Python for more details.