async for item in async_iterable:

Concurrency & Async

Meaning

Iterates asynchronously over an asynchronous iterable, awaiting each item as it becomes available. Use when you need to process items from an async source such as an async generator, network stream, or async queue without blocking the event loop.

Primary Function

Asynchronous iteration

Communicative Purpose

Process items from an async iterable sequentially while yielding control back to the event loop between items.

Pattern

async for item in async_iterable:

Core Structure

async for ... in ...:

Função primária

Asynchronous iteration

Propósito comunicativo

Process items from an async iterable sequentially while yielding control back to the event loop between items.

Situações de gatilho

Reading lines from an async file stream; consuming messages from an async queue; iterating over results of an async API call that returns an async generator.

Contextos

Python asyncio applications, web servers, data pipelines, any code using async/await.

Padrão

async for item in async_iterable:

Estrutura central

async for ... in ...:

Slots de substituição

item: identifier, async_iterable: expression returning an async iterable

Colocados típicos

await
async def
async with
async generator functions
async queues

Substituições comuns

Manual iteration with `aiter()` and `anext()` (more control but verbose)
async comprehension `[item async for item in async_iterable]` (collects all items eagerly
losing streaming benefit)

Erros comuns

Forgetting that the loop body must be async (cannot use regular functions that block); using a synchronous iterable causing TypeError; not handling cancellation properly.

Similar / contraste

Regular `for` loop (synchronous iteration); `async for` with `asyncio.gather` for concurrent processing; `while` loop with `await anext()`

Interferências

Coming from languages with only synchronous loops (e.g., Java, C#): may expect `for` to work on async iterables without `await`; need to remember to use `async for`.

Família do chunk

async iteration
async generators
async context managers
async comprehensions

Nuance

The loop will cancel if the enclosing task is cancelled; if the async iterable raises an exception, it propagates; avoid using `async for` with infinite async iterables without a break condition.

Efeito pragmático

Enables non-blocking processing of asynchronous data streams, preventing event loop stalls.

Dica de memória

Think 'async for' as 'await each item in turn'.

Nota

Requires Python 3.5+ due to PEP 492 (coroutines with async/await).

Upgrade path

async for item in async_iterable: await process(item)

Frequência: HighFormulaicidade: Semi-fixedTipo de construção: async for loopPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Medium-term

Examples

import asyncio import aiofiles async def main(): async with aiofiles.open('example.txt', mode='r') as f: async for line in f: print(line.strip()) asyncio.run(main())

import asyncio async def producer(queue): for i in range(5): await queue.put(i) await asyncio.sleep(0.1) await queue.put(None) # sentinel async def consumer(queue): async for item in queue: if item is None: break print('Received:', item) async def main(): queue = asyncio.Queue() await asyncio.gather(producer(queue), consumer(queue)) asyncio.run(main())

import asyncio async def async_number_generator(start, stop): for i in range(start, stop): await asyncio.sleep(0.2) # simulate async work yield i async def main(): async for number in async_number_generator(0, 3): print('Number:', number) asyncio.run(main())