On Fri, Nov 10, 2017 at 9:52 PM, Chris Jerdonek <chris.jerdo...@gmail.com> wrote: > Hi, I recently encountered a situation with asyncio where the stack > trace is getting truncated: an exception isn't getting chained as > expected. > > I was able to reduce it down to the code below. > > The reduced case seems like a pattern that can come up a lot, and I > wasn't able to find an issue on the CPython tracker, so I'm wondering > if I'm doing something wrong or if the behavior is deliberate.
I think what you're seeing is collateral damage from some known bugginess in the generator/coroutine .throw() method: https://bugs.python.org/issue29587 In trio I work around this by never using throw(); instead I send() in the exception and re-raise it inside the coroutine: https://github.com/python-trio/trio/blob/389f1e1e01b410756e2833cffb992fd1ff856ae5/trio/_core/_run.py#L1491-L1498 But asyncio doesn't do this -- when an asyncio.Task awaits an asyncio.Future and the Future raises, the exception is throw()n into the Task, triggering the bug: https://github.com/python/cpython/blob/e184cfd7bf8bcfd160e3b611d4351ca3ce52d9e2/Lib/asyncio/tasks.py#L178 (If you try profiling your code you may also see weird/impossible results in cases like this, because throw() also messes up stack introspection.) -n -- Nathaniel J. Smith -- https://vorpus.org _______________________________________________ Async-sig mailing list Async-sig@python.org https://mail.python.org/mailman/listinfo/async-sig Code of Conduct: https://www.python.org/psf/codeofconduct/
