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How do you properly propagate cancellation into an async generator when the consuming task is cancelled mid-iteration?

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Answer

When the task running an 'async for' loop is cancelled, asyncio.CancelledError is raised at the current 'await' point inside the generator (typically at the yield or an internal await) — a try/finally inside the generator still runs its cleanup correctly, since CancelledError propagates through the generator's frame just like any other exception.
async def stream_data():
    try:
        while True:
            data = await fetch_next_chunk()
            yield data
    except asyncio.CancelledError:
        print("Stream cancelled, cleaning up")
        raise  # re-raise to properly propagate cancellation
    finally:
        await cleanup_connection()
Real-world example Ensuring a streaming data pipeline cleans up its network connection correctly when the consuming task is cancelled (e.g., a request timeout).

Common follow-ups: Why is it important to re-raise CancelledError rather than swallowing it inside the except block?

Exception Handling
All 15 Async Generators & Async Context Managers questions