On Sat, Feb 27, 2021 at 1:09 PM Jim J. Jewett <jimjjew...@gmail.com> wrote:
> > In fact, if you're happy with RuntimeError here, making > > ExceptionGroup inherit from Exception (instead of > > BaseException) would do just as well -- after all RuntimeError > > is pretty arbitrary > > Agreed, and I think it should inherit from Exception. > > > (in fact, it's wrong, because the problem is a static bug in the > > code, not something that went wrong at run time). > > Something went wrong deep inside an individual task. The only clear > static bug is that the async library changed how it reported that, and my > except clause hasn't done the make-work to keep in step. > > > Let's see how this compares to the alternatives. First let's define > > three key examples. > > > Example 1: > > > try: > > raise ExceptionGroup(ValueError) > > except Exception: > > > Example 2: > > > try: > > raise ExceptionGroup(ValueError) > > except ValueError: > > Example 2(a) : > > try: > raise ExceptionGroup(ValueError,OtherError) > except ValueError: > > > Example 3: > > > try: > > raise ExceptionGroup(asyncio.CancelledError) > > except Exception: > > I would prefer that the except clause be executed in all of the examples, > but I admit that 2a is a problem, because it could end up silently losing > OtherError. And I admit getting example 2 to do the right thing if 2a > doesn't might be too much of a contortion. > > For example 3, I may be missing a subtle point, but I feel that by the > time you get to code which doesn't expect asyncio.CancelledError, then you > have already cancelled as far as you should. Cancelling may want to bubble > up through several other tasks, but it shouldn't kill the whole server, > just because the trampoline got sloppy. > If you're using 'except Exception:' and an asyncio.CancelledError (or trio.Cancelled) exception escapes, you're already dead, because those don't inherit from Exception, only from BaseException. And everything inherits from BaseException, including [Base]ExceptionGroup. -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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