import asyncio

loop = asyncio.get_event_loop()
q = asyncio.Queue(maxsize=1.2, loop=loop)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
.... and so on

It seems counter intuitive for my innocent eyes. As comparison with the traditional queue:

import queue
q = queue.Queue(maxsize=1.2)
q.put(1)
q.put(1)
q.put(1) -> blocking

Here is the patch to make the behaviour consistent with its sibling.

It looks strange to use a float as maxsize. I suggest to raise a TypeError in the constructor if the type is not int, or maybe to cast maxsize parameter to an int.

FWIW, this can also be resolved by fixing Queue.full to do "self.qsize() >= self._maxsize" instead of "self.qsize() == self._maxsize".

I generally don't like implicit casts as they break duck typing.

"It looks strange to use a float as maxsize." => It is. But the float could be coming programmatically. Float value interpreted as infinity could give a shock for some people.

"maybe to cast maxsize parameter to an int." => ceiling or flooring?

The patch looks fine to me.

New changeset ccfc13183fea by Victor Stinner in branch '3.4':
Issue #21723: asyncio.Queue: support any type of number (ex: float) for the
http://hg.python.org/cpython/rev/ccfc13183fea

New changeset a2f115bfa513 by Victor Stinner in branch 'default':
(Merge 3.4) Issue #21723: asyncio.Queue: support any type of number (ex: float)
http://hg.python.org/cpython/rev/a2f115bfa513

Thanks Vajrasky, I aplied your patch.

Change also pushed to Tulip (changeset 3a392e5328c0).