[issue39839] Non-working error handler when creating a task with assigning a variable

[Caleb Hattingh]

Caleb Hattingh <caleb.hattingh at gmail.com> added the comment:

Can reproduce also on 3.8. Another version that "works" (raises the exception) is

    task = loop.create_task(test())
    del task

Suggests there's something going on with reference counting or garbage collection. In the version that "doesn't work", the task exception only appears in the custom exception handler when the loop is stopped, not before. I've added a log message to show each second that passes, and the loop is stopped after 5 seconds:

    import asyncio
    import logging


    def handle_exception(loop, context):
        msg = context.get("exception", context["message"])
        logging.error("Caught exception: %s", msg)


    async def test():
        await asyncio.sleep(1)
        raise Exception("Crash.")


    def second_logger(loop, count) -> int:
        logging.warning(count)
        loop.call_later(1, lambda count=count: second_logger(loop, count + 1))


    def main():
        loop = asyncio.get_event_loop()
        loop.call_later(1, lambda: second_logger(loop, 0))
        loop.call_later(5, loop.stop)
        loop.set_exception_handler(handle_exception)
        task = loop.create_task(test())
        try:
            loop.run_forever()
        finally:
            loop.close()


    if __name__ == "__main__":
        main()

OUTPUT:

    $ py -3.8 -u bpo-issue39839.py
    WARNING:root:0
    WARNING:root:1
    WARNING:root:2
    WARNING:root:3
    WARNING:root:4
    ERROR:root:Caught exception: Crash.

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nosy: +cjrh

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39839>
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