Examples of Python decorators in action

decorators_examples.py

import random

"""
Python Decorators: Some Examples

This file contains a few examples of ways you can
use decorators. These are minimal examples that
should generalize usefully in many situations.

Also see: https://wiki.python.org/moin/PythonDecoratorLibrary
"""



# Example:
# Duplicate a call to a function.
# Rather than actually performing an action
# (like calling the function passed in),
# create a new function that carries out
# the sequences of actions desired.
# 
# The decorated function should perform an
# action (no return value). The next example
# covers functions with return values.

def duplicate_call(f):
    def g(*args,**kwargs):
        f(*args,**kwargs)
        f(*args,**kwargs)
    return g

@duplicate_call
def square(arg):
    print(arg*arg)



# Example:
# If we want to perform the action above
# (i.e., duplicate the function results),
# but the decorated function has a return
# value, we can compose the return values
# in the new function.

def triplicate(f):
    def g(*args,**kwargs):
        return (f(*args,**kwargs),f(*args,**kwargs),f(*args,**kwargs))
    return g

@triplicate
def cube(arg):
    return arg*arg*arg



# Example:
# Modify the return value of a function.
# Given an input function that returns integers,
# this decorator makes sure the input function
# never returns an integer larger than 10.

def volkswagen(f):
    def g(*args, **kwargs):
        return min(10, f(*args,**kwargs))
    return g

@volkswagen
def emissions_test():
    return random.randint(1,100)



if __name__=="__main__":
    
    square(5)
    # output:
    # 25
    # 25

    print(cube(5))
    # output:
    # (125, 125, 125)

    print("Emissions test result: %d"%(emissions_test()))
    # output:
    # Emissions test result: 9