await — Intermediate Examples

Pauses execution of an async coroutine until a result is available

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Await with error handling

Handling exceptions from awaited coroutines.

python
import asyncio

async def risky_operation(should_fail):
    await asyncio.sleep(0)
    if should_fail:
        raise ValueError("Something went wrong")
    return "success"

async def main():
    # try/except works with await
    try:
        result = await risky_operation(True)
    except ValueError as e:
        print(f"Caught: {e}")

    result = await risky_operation(False)
    print(f"Result: {result}")

    # Timeout with wait_for
    async def slow():
        await asyncio.sleep(10)
        return "done"

    try:
        result = await asyncio.wait_for(slow(), timeout=0.01)
    except asyncio.TimeoutError:
        print("Operation timed out!")

asyncio.run(main())
Expected Output
Caught: Something went wrong
Result: success
Operation timed out!

Exceptions from awaited coroutines propagate normally and can be caught with try/except. asyncio.wait_for adds timeout support.

Awaiting multiple things

Patterns for awaiting concurrent operations.

python
import asyncio

async def fetch(name, delay):
    await asyncio.sleep(delay)
    return f"{name}_data"

async def main():
    # Sequential (slow)
    a = await fetch("A", 0.01)
    b = await fetch("B", 0.01)
    print(f"Sequential: {a}, {b}")

    # Concurrent (fast)
    a, b = await asyncio.gather(
        fetch("A", 0.01),
        fetch("B", 0.01),
    )
    print(f"Concurrent: {a}, {b}")

    # as_completed: process in completion order
    tasks = [fetch("slow", 0.03), fetch("fast", 0.01), fetch("mid", 0.02)]
    for coro in asyncio.as_completed(tasks):
        result = await coro
        print(f"  Completed: {result}")

asyncio.run(main())

Sequential awaits run one after another. asyncio.gather runs them concurrently. as_completed yields results in the order they finish.

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