async — Intermediate Examples

Declares an asynchronous coroutine function or context manager

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Concurrent tasks with async

Running multiple async operations concurrently.

python
import asyncio

async def task(name, delay):
    print(f"  {name}: starting")
    await asyncio.sleep(delay)
    print(f"  {name}: done after {delay}s")
    return f"{name}-result"

async def main():
    # Run tasks concurrently with gather
    results = await asyncio.gather(
        task("A", 0.02),
        task("B", 0.01),
        task("C", 0.03),
    )
    print(f"Results: {results}")

asyncio.run(main())

asyncio.gather() runs multiple coroutines concurrently. Unlike threads, async switches tasks at await points, not preemptively.

Async iteration

Using async for and async generators.

python
import asyncio

async def countdown(name, n):
    for i in range(n, 0, -1):
        yield f"{name}: {i}"
        await asyncio.sleep(0)

async def main():
    async for msg in countdown("Timer", 3):
        print(msg)

    # Async comprehension
    values = [msg async for msg in countdown("Gen", 3)]
    print(values)

asyncio.run(main())
Expected Output
Timer: 3
Timer: 2
Timer: 1
['Gen: 3', 'Gen: 2', 'Gen: 1']

async for iterates over async generators (functions with yield and async). async comprehensions work just like regular comprehensions but inside async contexts.

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