aiochannel 1.4.0

asyncio Channels (closable queues) inspired by golang

aiochannel - AsyncIO Channel

Channel concept for asyncio.

Install

pip install aiochannel

Changelog

Changelog

Usage

Basics

Channel has a very similar API to asyncio.Queue. The key difference is that a channel is only considered "done" when it has been both closed and drained, so calling .join() on a channel will wait for it to be both closed and drained (Unlike Queue which will return from .join() once the queue is empty).

NOTE: Closing a channel is permanent. You cannot open it again.

import asyncio
from aiochannel import Channel

# ...

async def main():
    # A Channel takes a max queue size and an loop
    # both optional. loop is not recommended as
    # in asyncio is phasing out explicitly passed event-loop
    my_channel: Channel[str] = Channel(100)

    # You add items to the channel with
    await my_channel.put("my item")
    # Note that this can throw ChannelClosed if the channel
    # is closed, during the attempt at adding the item
    # to the channel. Also note that .put() will block until
    # it can successfully add the item.


    # Retrieving is done with
    my_item = await my_channel.get()
    # Note that this can also throw ChannelClosed if the
    # channel is closed before or during retrival.
    # .get() will block until an item can be retrieved.

    # Note that this requires someone else to close and drain
    # the channel.
    # Lastly, you can close a channel with `my_channel.close()`
    # In this example, the event-loop call this asynchronously
    asyncio.get_event_loop().call_later(0.1, my_channel.close)

    # You can wait for the channel to be closed and drained:
    await my_channel.join()

    # Every call to .put() after .close() will fail with
    # a ChannelClosed.
    # you can check if a channel is marked for closing with
    if my_channel.closed():
        print ("Channel is closed")

asyncio.run(main())

Like the asyncio.Queue you can also call non-async get and put:

    # non-async version of put
    my_channel.put_nowait(item)
    # This either returns None,
    # or raises ChannelClosed or ChannelFull

    # non-async version of get
    my_channel.get_nowait()
    # This either returns the next item from the channel
    # or raises ChannelEmpty or ChannelClosed
    # (Note that ChannelClosed emplies that the channel
    # is empty, but also that is will never fill again)

As of 0.2.0 Channel also implements the async iterator protocol. You can now use async for to iterate over the channel until it closes, without having to deal with ChannelClosed exceptions.

    # the channel might contain data here
    async for item in channel:
        print(item)
    # the channel is closed and empty here

which is functionally equivalent to

    while True:
        try:
            data = yield from channel.get()
        except ChannelClosed:
            break
        # process data here