# Improve asyncio.wait function
The original code creates the futures set two times.
We can create this set before, avoiding the second creation.
This new behaviour [breaks the aiokafka library](https://github.com/aio-libs/aiokafka/pull/672), because it gives an iterator to that function, so the second iteration become empty.
Automerge-Triggered-By: GH:1st1
Currently, if `asyncio.wait_for()` itself is cancelled it will always
raise `CancelledError` regardless if the underlying task is still
running. This is similar to a race with the timeout, which is handled
already.
When I was fixing bpo-32751 back in GH-7216 I missed the case when
*timeout* is zero or negative. This takes care of that.
Props to @aaliddell for noticing the inconsistency.
When an asyncio.Task is cancelled, the exception traceback now
starts with where the task was first interrupted. Previously,
the traceback only had "depth one."
Currently, if asyncio.wait_for() timeout expires, it cancels
inner future and then always raises TimeoutError. In case
those future is task, it can handle cancelation mannually,
and those process can lead to some other exception. Current
implementation silently loses thoses exception.
To resolve this, wait_for will check was the cancelation
successfull or not. In case there was exception, wait_for
will reraise it.
Co-authored-by: Roman Skurikhin <roman.skurikhin@cruxlab.com>
This will address the common mistake many asyncio users make:
an "except Exception" clause breaking Tasks cancellation.
In addition to this change, we stop inheriting asyncio.TimeoutError
and asyncio.InvalidStateError from their concurrent.futures.*
counterparts. There's no point for these exceptions to share the
inheritance chain.
In 3.9 we'll focus on implementing supervisors and cancel scopes,
which should allow better handling of all exceptions, including
SystemExit and KeyboardInterrupt
When the future returned by shield is cancelled, its completion callback of the
inner future is not removed. This makes the callback list of inner inner future
grow each time a shield is created and cancelled.
This change unregisters the callback from the inner future when the outer
future is cancelled.
https://bugs.python.org/issue35125
