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asyncio Channels (closable queues) inspired by golang

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aiochannel - AsyncIO Channel

Channel concept for asyncio.

requires Python 3.4.4+ (I think)





Channels are 90% 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
yield from 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 = yield from 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:
yield from my_channel.join()
# Note that this requires someone else to close and drain
# the channel.

# Lastly, you can close a channel with
# 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-coroutine get and put:

# non-coroutine version of put
# This either returns None,
# or raises ChannelClosed or ChannelFull

# non-coroutine version of get
# 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:
# the channel is closed and empty here

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