task.result()

Concurrency & Async

Meaning

Retrieves the return value of a completed Future or Task, re-raising any exception that occurred during execution. It addresses the need to explicitly extract an outcome when you cannot or choose not to use await, such as in callback-based or testing code. You reach for it when a Future is confirmed done and you need its value or want to surface its exception.

Primary Function

Concurrency result retrieval

Communicative Purpose

Obtain the outcome of an asynchronous operation.

Pattern

task.result(timeout=timeout)

Core Structure

...result(...)

Função primária

Concurrency result retrieval

Propósito comunicativo

Obtain the outcome of an asynchronous operation.

Situações de gatilho

Concurrent execution: retrieving a value from a completed Future after checking done(). Async testing: asserting the result of a finished Task in unit tests. Callback-based code: extracting the outcome inside an add_done_callback handler.

Contextos

concurrent.futures, asyncio, testing frameworks.

Padrão

task.result(timeout=timeout)

Estrutura central

...result(...)

Slots de substituição

task: Future or Task instance

Colocados típicos

await
add_done_callback
done()

Substituições comuns

future.result(timeout=seconds) for timed blocking waits on concurrent.futures.Future
await task for automatic exception propagation in async code

Erros comuns

Calling .result() before the Future is done — misconception that it blocks like Java's Future.get() — raises InvalidStateError on asyncio.Task or blocks indefinitely on concurrent.futures.Future. Forgetting to catch exceptions stored in the Future — assuming .result() always returns a value — causes unhandled exceptions to propagate unexpectedly. Using .result() instead of await in async code — misunderstanding that .result() participates in the event loop — can break cooperative scheduling. Passing timeout=0 expecting an instant check — misconception that zero means non-blocking poll — may still raise TimeoutError if the result is not immediately available.

Similar / contraste

await task (returns result or raises exception) vs .result() which raises InvalidStateError if not done.

Interferências

Coming from Java: confusion with Future.get() which blocks; .result() raises if not done rather than blocking.

Família do chunk

Future.result
Task.result
asyncio.wait_for

Nuance

Never call .result() on an asyncio.Task before confirming it is done — it raises InvalidStateError rather than blocking. On concurrent.futures.Future, .result() blocks the calling thread until the computation finishes, potentially stalling indefinitely without a timeout. The timeout parameter exists only on concurrent.futures.Future.result(), not on asyncio.Task.result().

Efeito pragmático

Allows explicit retrieval of result with precise error handling.

Dica de memória

Get the fruit of the future.

Nota

Use .result() only after confirming the Future/Task is done; prefer await for automatic exception propagation; handle InvalidStateError and use the timeout argument for timed waits.

Upgrade path

Use await task for automatic exception propagation.

Frequência: MediumFormulaicidade: Semi-fixedTipo de construção: method callPrioridade de aquisição: Recognition firstPrioridade de output: BothTag de espaçamento: Medium-term

Examples

from concurrent.futures import ThreadPoolExecutor def work(x): return x * x with ThreadPoolExecutor() as executor: future = executor.submit(work, 5) # Do other work... result = future.result() # returns when done print(result)

import asyncio async def fetch(): await asyncio.sleep(1) return 42 async def main(): task = asyncio.create_task(fetch()) await asyncio.sleep(0.5) if task.done(): result = task.result() print(result) else: print("not yet done") asyncio.run(main())

from unittest.mock import Mock future = Mock() future.result.return_value = "success" # Simulate code that uses future result = future.result() assert result == "success"