Simple decorator examples

simple_timer_decorator.py

import time
import functools

def timer(func):
	#Decorator function takes the decorated function as parameter

	@functools.wraps(func)
	def wrapper(*args, **kwargs):
		#the replacement function to be used

		#Here we do stuff that is necessary before the function is run
		start_time = time.time()

		# Running the actual function and storing the result
		result = func(*args, **kwargs)

		# Doing stuff after function
		elapsed_time = time.time() - start_time
		print("Time taken to run {0}: {1} seconds".format(func.__name__,elapsed_time ))

		#return the result of a function
		return result


	# return the replacement function
	return wrapper

@timer
def foo(range_end):
	"""
	A test function that returns a list of integers from 0 to range_end.
	"""
	return [i for i in range(range_end)]

foo(10**5)

# if I hadn't used @functools.wraps(func) decorator for the wrapper, 
# these calls would have returned "wrapper" and no docstring instead of `foo` and its docstring.
print(foo.__name__)
print(foo.__doc__)