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: startingconsumer 0: waiting for itemconsumer 1: startingconsumer 1: waiting for itemproducer: startingproducer: added task 0 to the queueproducer: added task 1 to the queueconsumer 0: has item 0consumer 1: has item 1producer: added task 2 to the queueproducer: added task 3 to the queueconsumer 0: waiting for itemconsumer 0: has item 2producer: added task 4 to the queueconsumer 1: waiting for itemconsumer 1: has item 3producer: added task 5 to the queueproducer: adding stop signals to the queueconsumer 0: waiting for itemconsumer 0: has item 4consumer 1: waiting for itemconsumer 1: has item 5producer: waiting for queue to emptyconsumer 0: waiting for itemconsumer 0: has item Noneconsumer 0: endingconsumer 1: waiting for itemconsumer 1: has item Noneconsumer 1: endingproducer: ending