Issue 36403: AsyncIterator on 3.7: aiter no longer honors finally blocks (original) (raw)

Created on 2019-03-23 00:15 by asksol, last changed 2022-04-11 14:59 by admin.

Messages (7)
msg338630 - (view)	Author: Ask Solem (asksol)	Date: 2019-03-23 00:15
We use finally blocks in ``__aiter__`` like this: ``` class AsyncFinallyIterator: def __aiter__(self): for i in range(10): try: yield i finally: print('FINALLY') ``` Attached is a test for both iterators and async iterators. The tests pass on Python 3.6, but only the non-async iterator test pass under Python 3.7. Thanks for your attention! This worked perfectly well in Python 3.6, but stopped working in Python 3.7. I also verified that Iterator supports the same construct (and this works in both Python 3.6 and 3.7): ``` class FinallyIterator: def __iter__(self): for i in range(10): try: yield i finally: print('FINALLY') ```
msg338638 - (view)	Author: Karthikeyan Singaravelan (xtreak) *	Date: 2019-03-23 01:02
The attached script fails on master too. On bisecting could this be possibly caused due to 41e5ec377b (bpo-34769) ? Tagging Ned since it was introduced from 3.7.1rc2 and also backported to 3.6 . ➜ cpython git:(41e5ec377b) git checkout 41e5ec377b && make -s -j4 > /dev/null HEAD is now at 41e5ec377b bpo-34769: Thread safety for _asyncgen_finalizer_hook(). (GH-9716) ➜ cpython git:(41e5ec377b) ./python.exe ../backups/bpo36403.py F. ====================================================================== FAIL: test_main (__main__.TestAsyncIteratorFinally) ---------------------------------------------------------------------- Traceback (most recent call last): File "../backups/bpo36403.py", line 30, in test_main self.assertTrue(it.finally_executed) AssertionError: False is not true ---------------------------------------------------------------------- Ran 2 tests in 0.002s FAILED (failures=1) ➜ cpython git:(41e5ec377b) git checkout 41e5ec377b~1 && make -s -j4 > /dev/null Previous HEAD position was 41e5ec377b bpo-34769: Thread safety for _asyncgen_finalizer_hook(). (GH-9716) HEAD is now at 0ce31d340b bpo-32962: Fix test_gdb failure in debug build with -mcet -fcf-protection -O0 (GH-9656) ➜ cpython git:(0ce31d340b) ./python.exe ../backups/bpo36403.py .. ---------------------------------------------------------------------- Ran 2 tests in 0.003s OK
msg338642 - (view)	Author: Ask Solem (asksol)	Date: 2019-03-23 05:35
Ah, so the extra call_soon means it needs a: [code] loop.run_until_complete(asyncio.sleep(0))``` [/code] before the self.assertTrue(it.finally_executed) to finish executing agen.close(). Why is create_task different? Does it execute an iteration of the generator immediately? Seems good for this behavior to be consistent, but not sure how difficult that would be.
msg338647 - (view)	Author: Ask Solem (asksol)	Date: 2019-03-23 06:29
Perhaps we could add a self._finally to the event loop itself? Like loop._ready, but a list of callbacks run_until_complete will call before returning?
msg345805 - (view)	Author: Ned Deily (ned.deily) *	Date: 2019-06-17 07:34
Ping. This was marked as a 3.7regression. Is a change needed?
msg345808 - (view)	Author: Andrew Svetlov (asvetlov) *	Date: 2019-06-17 07:47
From my understanding yield inside __aiter__ is a forbidden construction. Even if parser allows it the statement doesn't make any sense. I'm very interested to hear Yuri opinion.
msg371341 - (view)	Author: Ned Deily (ned.deily) *	Date: 2020-06-12 08:32
I note this is marked as a 3.7regression and still open. Since the cutoff for the final 3.7 bugfix mode release is in a few days, I'm assuming this means that 3.7 users will have to live with this regression. If you feel that is a problem, speak up now.