Queue
- Python course
- Advanced
- Lesson 33/83
- 5 min
Learn producer-consumer with asyncio.Queue.
Queue
asyncio.Queue provides safe data passing between coroutines. A producer puts data with put; a consumer takes it with get. One waits while the other works.
import asyncio
q = asyncio.Queue()
await q.put(1)
value = await q.get()Queue is used for buffered communication. If the producer is fast and the consumer is slow, the queue acts as a buffer; and vice versa. When full, put waits; when empty, get waits.
Producer-consumer pattern
Queue implements the classic producer-consumer pattern. A producer coroutine generates data and puts it in the queue with await q.put(item); a consumer takes data with await q.get() and processes it.
When the producer finishes, it can put a sentinel like q.put(None); the consumer stops on seeing it. Multiple consumers are supported; each runs in a separate Task.
Queue makes this pattern safe and scalable in asyncio; no lock is needed.
Practice Producer-consumer with Queue
Start with import asyncio. The function async def producer(q) does await q.put(42) and await q.put(None). The function async def consumer(q) reads value = await q.get() and returns it. Inside async def main() build q = asyncio.Queue(), call asyncio.gather(producer(q), consumer(q)) and return it. Add print(asyncio.run(main())).
Starter code
# import the asyncio module
# producer(q): put 42 and None
# consumer(q): get the value and return it
# main: create Queue, run both via gather, print resultSample solution
import asyncio
async def producer(q):
await q.put(42)
await q.put(None)
async def consumer(q):
value = await q.get()
return value
async def main():
q = asyncio.Queue()
return await asyncio.gather(producer(q), consumer(q))
print(asyncio.run(main()))Expected output
[None, 42]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the Queue methods
| Term | Meaning |
|---|---|
q.put(item) |
Puts data |
q.get() |
Gets data |
q.qsize() |
Returns size |
await q.put |
Waits for room |
2 What does await q.get() do when the Queue is empty?
- Returns None immediately
- Raises an error
- Closes the program
- Waits until data arrives Correct answer
Explanation: q.get() waits until data arrives; await frees the event loop.
3 Queue import and definition
import asyncio
q = asyncio.____()import asyncio
q = asyncio.Queue()Explanation: asyncio.Queue() creates a new queue.