aiostream

Generator-based operators for asynchronous iteration

Synopsis

aiostream_ provides a collection of stream operators that can be combined to create asynchronous pipelines of operations.

It can be seen as an asynchronous version of itertools_, although some aspects are slightly different. Essentially, all the provided operators return a unified interface called a stream. A stream is an enhanced asynchronous iterable providing the following features:

Operator pipe-lining - using pipe symbol |
Repeatability - every iteration creates a different iterator
Safe iteration context - using async with and the stream method
Simplified execution - get the last element from a stream using await
Slicing and indexing - using square brackets []
Concatenation - using addition symbol +

Stream operators

The stream operators_ are separated in 7 categories:

+--------------------+---------------------------------------------------------------------------------------+ | creation | iterate, preserve, just, call, empty, throw, never, repeat, count, range | +--------------------+---------------------------------------------------------------------------------------+ | transformation | map, enumerate, starmap, cycle, chunks | +--------------------+---------------------------------------------------------------------------------------+ | selection | take, takelast, skip, skiplast, getitem, filter, until, takewhile, dropwhile | +--------------------+---------------------------------------------------------------------------------------+ | combination | map, zip, merge, chain, ziplatest | +--------------------+---------------------------------------------------------------------------------------+ | aggregation | accumulate, reduce, list | +--------------------+---------------------------------------------------------------------------------------+ | advanced | concat, flatten, switch, concatmap, flatmap, switchmap | +--------------------+---------------------------------------------------------------------------------------+ | timing | spaceout, timeout, delay | +--------------------+---------------------------------------------------------------------------------------+ | miscellaneous | action, print_ | +--------------------+---------------------------------------------------------------------------------------+

Demonstration

The following example demonstrates most of the streams capabilities:

.. code:: python

import asyncio
from aiostream import stream, pipe

async def main():

    # Create a counting stream with a 0.2 seconds interval
    xs = stream.count(interval=0.2)

    # Operators can be piped using '|'
    ys = xs | pipe.map(lambda x: x**2)

    # Streams can be sliced
    zs = ys[1:10:2]

    # Use a stream context for proper resource management
    async with zs.stream() as streamer:

        # Asynchronous iteration
        async for z in streamer:

            # Print 1, 9, 25, 49 and 81
            print('->', z)

    # Streams can be awaited and return the last value
    print('9² = ', await zs)

    # Streams can run several times
    print('9² = ', await zs)

    # Streams can be concatenated
    one_two_three = stream.just(1) + stream.range(2, 4)

    # Print [1, 2, 3]
    print(await stream.list(one_two_three))

# Run main coroutine
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
loop.close()

More examples are available in the example section_ of the documentation.