import time


def fibonacci():
    '''Good old fibonacci'''
    a, b = 0, 1
    while True:
       yield b
       # Sleep to be able to see the numbers generation
       time.sleep(1)
       a, b = b, a+b

cool_iterator = (n for n in range(1000000000))

def coroutine():
    # dumb coroutine example
    x = 0
    while True:
        x = (yield x) + x