import functools, time, datetime

@functools.lru_cache()
def getCurrentTime():
    # This nondeterministic function returns different values each time
    # it's called.
    return datetime.datetime.now()

@functools.lru_cache()
def printMessage():
    # This function displays a message on the screen as a side effect.
    print('Hello, world!')

print('Getting the current time twice:')
print(getCurrentTime())
print('Waiting two seconds...')
time.sleep(2)
print(getCurrentTime())

print()

print('Displaying a message twice:')
printMessage()
printMessage()