[New-bugs-announce] [issue25291] better Exception message for certain task termination scenario

[Oleg]

New submission from Oleg:

the weird condition in the code 
causes the task to end with double exception, hard
to understand what really had happened. 

 
producing output like that:


|    i am task..
|    i keep working
|    Exception in callback Task._step()
|    handle: <Handle Task._step()>
|    Traceback (most recent call last):
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/tasks.py", line 239, in _step
|        result = coro.send(value)
|    StopIteration
|
|    During handling of the above exception, another exception occurred:
|
|    Traceback (most recent call last):
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/events.py", line 125, in _run
|        self._callback(*self._args)
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/tasks.py", line 241, in _step
|        self.set_result(exc.value)
|      File "/home/http/Python-3.5.0/lib/python3.5/asyncio/futures.py", line 335, in set_result
|        raise InvalidStateError('{}: {!r}'.format(self._state, self))
|    asyncio.futures.InvalidStateError: FINISHED: <Task finished coro=<task() done, defined at test_aio_exception.py:4> exception=RuntimeError('something bad',)>


it would be good to improve that shutdown procedure 
to pinpoint real reason why and when it got into broken state.

additional info can be found here:
https://groups.google.com/forum/#!topic/python-tulip/-EcYtJXDvSo

----------
components: asyncio
files: test_aio_exception.py
messages: 252049
nosy: gvanrossum, haypo, ovex, yselivanov
priority: normal
severity: normal
status: open
title: better Exception message for certain task termination scenario
type: enhancement
versions: Python 3.5
Added file: http://bugs.python.org/file40650/test_aio_exception.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25291>
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