asyncio.wait_for

Concurrency & Async

Meaning

asyncio.wait_for wraps an awaitable with a timeout, cancelling it and raising TimeoutError if the operation does not complete within the given time. It is used to bound the execution time of asynchronous operations and avoid indefinite hanging.

Primary Function

Concurrency control

Communicative Purpose

Ensures that a coroutine completes within a specified time limit, raising TimeoutError otherwise.

Pattern

asyncio.wait_for(awaitable, timeout=timeout_seconds)

Core Structure

asyncio.wait_for(...)

Função primária

Concurrency control

Propósito comunicativo

Ensures that a coroutine completes within a specified time limit, raising TimeoutError otherwise.

Situações de gatilho

Waiting for a network request that might stall Limiting the duration of a background task Preventing an async operation from hanging indefinitely

Contextos

Python asyncio applications, web servers, async libraries, any code that uses async/await and needs bounded execution.

Padrão

asyncio.wait_for(awaitable, timeout=timeout_seconds)

Estrutura central

asyncio.wait_for(...)

Slots de substituição

awaitable: an awaitable object (coroutine, Task); timeout_seconds: numeric timeout (int or float).

Colocados típicos

asyncio.create_task
asyncio.gather
try/except TimeoutError.

Substituições comuns

Using asyncio.shield to prevent cancellation
or the asyncio.timeout() context manager (Python 3.11+).

Erros comuns

Forgetting to await the result of wait_for. Passing a non‑awaitable object. Using timeout=0 which raises TimeoutError immediately. Not handling the TimeoutError exception.

Similar / contraste

asyncio.shield (protects from cancellation), asyncio.wait (waits for multiple awaitables with a timeout).

Interferências

Coming from threading: similar timeout concepts exist, but asyncio.wait_for cancels the inner awaitable on timeout, whereas threading timers usually just interrupt a blocking call.

Família do chunk

asyncio.wait
asyncio.shield
asyncio.timeout

Nuance

Do not use when you need the operation to continue after a timeout (use shield or a separate task); setting a very short timeout can cause excessive cancellations and CPU overhead; a timeout of None disables timeout but also disables automatic cancellation, requiring manual cancellation.

Efeito pragmático

Prevents unbounded waiting, making async code resilient to stalled or slow operations.

Dica de memória

"Wait with a guardrail" – think of a safety net that pulls the operation back if it takes too long.

Nota

Available since Python 3.4; Python 3.11+ also provides the asyncio.timeout() context manager as a more flexible alternative.

Upgrade path

Use asyncio.timeout() context manager for more complex timeout handling, or asyncio.wait with return_when=FIRST_COMPLETED for multi‑awaitable scenarios.

Frequência: MediumFormulaicidade: Semi-fixedTipo de construção: function callPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Medium-term

Examples

import asyncio import aiohttp async def fetch_url(session, url): async with session.get(url) as resp: return await resp.text() async def main(): async with aiohttp.ClientSession() as session: try: html = await asyncio.wait_for(fetch_url(session, 'https://httpbin.org/delay/10'), timeout=5) print('Fetched:', html[:50]) except asyncio.TimeoutError: print('Request timed out') asyncio.run(main())

import asyncio async def slow_task(): await asyncio.sleep(8) return 'done' async def main(): try: result = await asyncio.wait_for(slow_task(), timeout=3) print(result) except asyncio.TimeoutError: print('Task took too long') asyncio.run(main())

import asyncio async def work(): await asyncio.sleep(2) return 'completed' async def main(): # Shield prevents cancellation of the inner awaitable on timeout try: result = await asyncio.wait_for(asyncio.shield(work()), timeout=1) print('Result:', result) except asyncio.TimeoutError: print('Timeout, but work() continues in background') # work() still runs; we could await it later if desired asyncio.run(main())