[New-bugs-announce] [issue26221] asynco run_in_executor swallows StopIteration

[Ian Kelly]

New submission from Ian Kelly:

I was playing around with this class for adapting regular iterators to async iterators using BaseEventLoop.run_in_executor:


import asyncio

class AsyncIteratorWrapper:

    def __init__(self, iterable, loop=None, executor=None):
        self._iterator = iter(iterable)
        self._loop = loop or asyncio.get_event_loop()
        self._executor = executor

    async def __aiter__(self):
        return self

    async def __anext__(self):
        try:
            return await self._loop.run_in_executor(
                    self._executor, next, self._iterator)
        except StopIteration:
            raise StopAsyncIteration


Unfortunately this fails because when next raises StopIteration, run_in_executor swallows the exception and just returns None back to the coroutine, resulting in an infinite iterator of Nones.

----------
components: asyncio
messages: 259036
nosy: gvanrossum, haypo, ikelly, yselivanov
priority: normal
severity: normal
status: open
title: asynco run_in_executor swallows StopIteration
versions: Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26221>
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