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How to use decorators in Python

gcptutorials.com Python

Decorator is a function returning another function, it is applied as a function transformation using the @wrapper syntax. Common examples for decorators are classmethod() and staticmethod(). Lets understand decorators with some examples.

To understand decorators we will create two functions, one function will work as a decorator and other function will be decorated by decorator.

  • function execution_time will work as decorator
  • function decorated_func will be decorated with execution_time

    • Define execution_time and decorated_func

    
def decorated_func():
    dl =[]
    for i in range(100):
        dl.append(i)


def execution_time(func):
    def wrapper():
        start = time.time()
        func()
        end = time.time()
        msg = f"time elapsed in executing func is { end - start}"
        return msg
    return wrapper

    As from the function definition we can see execution_time function calculates time taken by the decorated_func, lets use @ syntax to decorate the decorate_func

    
import time

def execution_time(func):
    def wrapper():
        start = time.time()
        func()
        end = time.time()
        msg = f"time elapsed in executing func is { end - start}"
        return msg
    return wrapper

@execution_time
def decorated_func():
    dl =[]
    for i in range(100):
        dl.append(i)

elapsed_time = decorated_func()
print(elapsed_time)

    Output 

    
time elapsed in executing func is 0.0010013580322265625

    Now, instead of hard coding "100" in range of decorated_func, use argument to provide different values, lets see how decorator would be changed to accommodate this.

    
import time

def execution_time(func):
    def wrapper(*args, **kwargs):
        start = time.time()
        func(*args, **kwargs)
        end = time.time()
        msg = f"time elapsed in executing func is { end - start}"
        return msg
    return wrapper

@execution_time
def decorated_func(k):
    dl =[]
    for i in range(k):
        dl.append(i)

elapsed_time = decorated_func(100000)
print(elapsed_time)

    Output:

    
time elapsed in executing func is 0.020013809204101562

    So with the use of *args and **kwargs we are able to pass argument to the decorated functions.

    Category: Python