import asyncio 
 
 
async def consumer(n, q): 
 print('consumer {}: starting'.format(n)) 
 while True: 
  print('consumer {}: waiting for item'.format(n)) 
  item = await q.get() 
  print('consumer {}: has item {}'.format(n, item)) 
  if item is None: 
   # None is the signal to stop. 
   q.task_done() 
   break 
  else: 
   await asyncio.sleep(0.01 * item) 
   q.task_done() 
 print('consumer {}: ending'.format(n)) 
 
 
async def producer(q, num_workers): 
 print('producer: starting') 
 # Add some numbers to the queue to simulate jobs 
 for i in range(num_workers * 3): 
  await q.put(i) 
  print('producer: added task {} to the queue'.format(i)) 
 # Add None entries in the queue 
 # to signal the consumers to exit 
 print('producer: adding stop signals to the queue') 
 for i in range(num_workers): 
  await q.put(None) 
 print('producer: waiting for queue to empty') 
 await q.join() 
 print('producer: ending') 
 
 
async def main(loop, num_consumers): 
 # Create the queue with a fixed size so the producer 
 # will block until the consumers pull some items out. 
 q = asyncio.Queue(maxsize=num_consumers) 
 
 # Scheduled the consumer tasks. 
 consumers = [ 
  loop.create_task(consumer(i, q)) 
  for i in range(num_consumers) 
 ] 
 
 # Schedule the producer task. 
 prod = loop.create_task(producer(q, num_consumers)) 
 
 # Wait for all of the coroutines to finish. 
 await asyncio.wait(consumers + [prod]) 
 
 
event_loop = asyncio.get_event_loop() 
try: 
 event_loop.run_until_complete(main(event_loop, 2)) 
finally: 
 event_loop.close() 

consumer 0: starting
consumer 0: waiting for item
consumer 1: starting
consumer 1: waiting for item
producer: starting
producer: added task 0 to the queue
producer: added task 1 to the queue
consumer 0: has item 0
consumer 1: has item 1
producer: added task 2 to the queue
producer: added task 3 to the queue
consumer 0: waiting for item
consumer 0: has item 2
producer: added task 4 to the queue
consumer 1: waiting for item
consumer 1: has item 3
producer: added task 5 to the queue
producer: adding stop signals to the queue
consumer 0: waiting for item
consumer 0: has item 4
consumer 1: waiting for item
consumer 1: has item 5
producer: waiting for queue to empty
consumer 0: waiting for item
consumer 0: has item None
consumer 0: ending
consumer 1: waiting for item
consumer 1: has item None
consumer 1: ending
producer: ending