async-queues.md

Python by Example: Async Queues

asyncio.Queue is a FIFO queue for passing data between async tasks. Producers put items; consumers get them. Both put() and get() are coroutines—they yield while waiting. Use queues when one task produces data and another consumes it, like a pipeline. Use None or a sentinel to signal "no more items."

What you'll learn:

• Creating and using asyncio.Queue
• Producer-consumer pattern with async
• Signaling completion

import asyncio


async def producer(queue):
    for i in range(3):
        await queue.put(i)
        print(f"Produced {i}")
    await queue.put(None)  # Signal done


async def consumer(queue):
    while True:
        item = await queue.get()
        if item is None:
            break
        print(f"Consumed {item}")
        queue.task_done()


async def main():
    q = asyncio.Queue()
    await asyncio.gather(producer(q), consumer(q))


asyncio.run(main())

The producer puts 0, 1, 2, then None to signal "done." The consumer stops when it sees None. task_done() marks the item as processed (useful with join()).

To run this program:

$ python source/async-queues.py
Produced 0
Consumed 0
Produced 1
Consumed 1
Produced 2
Consumed 2

Tip: For multiple consumers, put one None per consumer, or use a different sentinel strategy.

Try it: Add a second consumer and see how they share the work.

Source: async-queues.py

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