Presentation

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 +

Requirements

The stream operators rely heavily on asynchronous generators (PEP 525):

• python >= 3.6

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:

import asyncio

from aiostream import pipe, stream


def square(x: int, *_: int) -> int:
    return x**2


async def main() -> None:
    # 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(square)

    # 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
asyncio.run(main())

More examples are available in the example section.

References

This library is inspired by:

• PEP 525: Asynchronous Generators

• Rx - Reactive Extensions

• aioreactive - Async/await reactive tools for Python 3.5+

• itertools - Functions creating iterators for efficient looping