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asyncio Channels (closable queues) inspired by golang

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aiochannel - AsyncIO Channel

Channel concept for asyncio.

requires Python 3.5+

PyPI link

Install

pip install aiochannel

Usage

Basics

Most of the Channel code is from asyncio.Queue, and the API is very similar. 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

# ...

# A Channel takes a max queue size and an loop
# both optional
my_channel = Channel(100, asyncio.get_event_loop())

# 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.


# You can wait for the channel to be closed and drained:
await my_channel.join()
# Note that this requires someone else to close and drain
# the channel.

# Lastly, you can close a channel with
my_channel.close()
# 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")

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

Noteworthy changes

0.2.0

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

See the async for example.

0.2.3

Channel proxies it’s __iter__ to the underlying queue implementation’s __iter__ (which by default is collections.deque), meaning that you are now able to iterate channel values (which also enables list(channel)).

1.0.0

Dropping 3.4’s @coroutine annotations. Everything is now defined with async.

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