asyncio.wait_for

Concurrency & Async

Meaning

Wraps an awaitable with a deadline, cancelling it and raising TimeoutError if it exceeds the specified timeout in seconds. Addresses the pain point of coroutines that may hang indefinitely on unresponsive network services or stalled subprocesses. Reached for whenever an async operation must be bounded in time to maintain system responsiveness or implement fallback logic.

Primary Function

Enforce a timeout on awaiting an awaitable, cancelling it on timeout.

Communicative Purpose

Prevents indefinite blocking by enforcing a maximum wait time on an awaitable, cancelling it on expiry.

Pattern

asyncio.wait_for(awaitable, timeout)

Core Structure

asyncio.wait_for(..., ...)

Função primária

Enforce a timeout on awaiting an awaitable, cancelling it on timeout.

Propósito comunicativo

Prevents indefinite blocking by enforcing a maximum wait time on an awaitable, cancelling it on expiry.

Situações de gatilho

Network clients: awaiting a response from a potentially unresponsive server. Subprocess management: reading output from a child process that may stall. User interaction: waiting for input with a grace period before falling back to defaults.

Contextos

Asynchronous I/O, network clients, user input handling, any async operation where unbounded waiting is undesirable.

Padrão

asyncio.wait_for(awaitable, timeout)

Estrutura central

asyncio.wait_for(..., ...)

Slots de substituição

awaitable: coroutine, Task, or Future, timeout: float seconds or None

Colocados típicos

asyncio
Task
Future
coroutine
timeout
TimeoutError
cancel

Substituições comuns

awaitable: any coroutine
Task
Future
timeout: float/int seconds or None

Erros comuns

Forgetting to catch TimeoutError — cause: assuming the function returns None on timeout; consequence: unhandled exception crashes the coroutine. Passing a non-awaitable object — cause: misunderstanding that wait_for requires an awaitable, not a plain function; consequence: TypeError at runtime. Setting a negative timeout — cause: assuming negative values mean no timeout; consequence: ValueError raised. Assuming the inner task is not cancelled — cause: not reading the cancellation semantics; consequence: cleanup code in the inner coroutine may run unexpectedly or not at all.

Similar / contraste

asyncio.wait (with timeout parameter), asyncio.shield (protects from cancellation), asyncio.sleep (simple delay), asyncio.timeout context manager (Python 3.11+)

Interferências

Coming from Go: may assume a timeout merely returns an error without cancelling the goroutine — asyncio.wait_for cancels the awaitable, triggering its cleanup.

Família do chunk

asyncio-wait-for

Nuance

Do not use wait_for when you need the inner task to survive cancellation — use asyncio.shield instead. The timeout is checked at the next yield point, so a coroutine that never yields cannot be interrupted mid-execution. On timeout, the inner awaitable is cancelled first; if cancellation cleanup takes time, the actual delay before TimeoutError may exceed the specified timeout.

Efeito pragmático

Imposes a bounded waiting period, preventing indefinite blocking and allowing fallback or timeout handling.

Dica de memória

Wait for this coroutine but give up after X seconds.

Nota

Prefer the structured asyncio.timeout() context manager (Python 3.11+) for clearer timeout scopes; wait_for remains useful for simple one‑off timeouts.

Upgrade path

Consider using asyncio.timeout() context manager (Python 3.11+) or asyncio.wait with a timeout parameter for more flexible timeout handling.

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

Examples

import asyncio async def fetch_data(url): await asyncio.sleep(5) return f"data from {url}" async def main(): try: result = await asyncio.wait_for(fetch_data("https://api.example.com"), timeout=3.0) print(result) except asyncio.TimeoutError: print("Request timed out, using cached data") asyncio.run(main())

import asyncio async def run_command(cmd): process = await asyncio.create_subprocess_exec(*cmd, stdout=asyncio.subprocess.PIPE) try: stdout, _ = await asyncio.wait_for(process.communicate(), timeout=10.0) return stdout.decode() except asyncio.TimeoutError: process.kill() await process.wait() return "Command timed out" async def main(): output = await run_command(["ping", "-c", "5", "example.com"]) print(output) asyncio.run(main())

import asyncio async def get_user_choice(): loop = asyncio.get_event_loop() print("Press Enter within 5 seconds to continue...") try: await asyncio.wait_for(loop.run_in_executor(None, input), timeout=5.0) return True except asyncio.TimeoutError: print("No input received, proceeding with defaults") return False async def main(): confirmed = await get_user_choice() print(f"User confirmed: {confirmed}") asyncio.run(main())