Async Iterators

AsyncIterable and AsyncIterator got introduced in conjunction with the async/await syntax in PEP 492 with Python 3.5.

AsyncIterators in conjunction with the new async for statement allow iterating over items that have been requested asynchronously. That means the async for loop may suspend on every iteration until the next iteration result is available.

AsyncIterable

class AsyncIterable:
    def __aiter__(self) -> AsyncIterator:
        """
        Return an AsyncIterator
        """

AsyncIterator

class AsyncIterator(AsyncIterable):
    async def __anext__(self) -> Any:
        """
        Return the next item or raise StopAsyncIteration when exhausted.
        """

async for

A new async for statement is used in conjunction with AsyncIterators.

async for TARGET in ITER:
    BLOCK
else:
    BLOCK2

iterable = (ITER)
iter = iterable.__aiter__()
running = True
while running:
    try:
        TARGET = await iter.__anext__()
    except StopAsyncIteration:
        running = False
    else:
        BLOCK
else:
    BLOCK2

Summary

• AsyncIterator can be used in conjunction with the async for statement.

• AsyncIterator can suspend on each iteration, for example to request new data from the network.