#!/usr/bin/env python3

import asyncio

class ArbitraryException(Exception):
    pass

async def consumer(p):
    while True:
        try:
            product = yield # unpack the sent product, consume somehow
            print("product was {}, okok".format(product))
        except ArbitraryException as e:
            print("cons stopping")
            break           # jump out of consumption loop

async def producer(n):
    c = yield               # yield to get consumer passed in
    for i in range(n):
        await c.asend(i)    # produce portion of coroutine
    try:
        await c.athrow(ArbitraryException())
    except StopAsyncIteration:
        print("prod stopping")

async def main():
    p = producer(10)        # Create coroutine object producer
    c = consumer(p)         # Create coroutine object consumer
    await p.asend(None)     # start producer instance
    await c.asend(None)     # start consumer instance
    try:
        await p.asend(c)    # send producer a consumer, wait for execution to return from it.
    except StopAsyncIteration:
        print("main returning")

if __name__ == '__main__':
    try:
        loop = asyncio.get_event_loop()
        loop.run_until_complete(main())
    finally:
        print("program exiting")
        loop.close()

# Sample Output:
"""product was 0, okok
product was 1, okok
product was 2, okok
product was 3, okok
product was 4, okok
product was 5, okok
product was 6, okok
product was 7, okok
product was 8, okok
product was 9, okok
cons stopping
prod stopping
main returning
program exiting"""