Hi Paul,
On Wed, Mar 3, 2021 at 2:20 PM Paul Moore <p.f.mo...@gmail.com> wrote:
>
> 1. Having now read the PEP, I don't actually see a use case for
> grouping BaseExceptions. Why would anyone catch KeyboardInterrupt or
> SystemExit and wrap them in a BaseExceptionGroup anyway? It seems to
> me that the right thing to do, even in async or parallel code, is to
> just propogate the KeyboardInterrupt/SystemExit up to the main
> program. Losing a ValueError that happened at the exact same time as
> the user pressed Ctrl-C seems like it's not going to be a problem in
> practice...
>
It is possible that your program wants to do something other than just
terminate when it gets a KeyboardInterrupt. Otherwise why does the
interpreter bother propagating the KeyboardInterrupt rather than just
terminate the program there and then?
And the ValueError you lost may be some other error type that involves
cleanup.
If you do this:
try:
async.gather(...) # raises BaseExceptionGroup( DoCleanup(),
KeyboardInterrupt())
except * DoCleanup:
do_cleanup() # log stuff, send notifications, close sockets, whatever
That will do the cleanup in addition to propagating a
BaseExceptionGroup(KeyboardInterrupt())
Also, KeyboardInterrupt/SystemExit are not the only BaseExceptions.
> 2. Given the above, why even have a means of grouping BaseExceptions
> at all? Why not just have ExceptionGroup that can only catch instances
> of Exception?
>
Because the IGotInterrupted alternative involves wrapping a BaseException
by an Exception, which is not something we should push people into doing
(it's not that different from allowing ExceptionGroup to wrap
BaseExceptions directly).
What's the harm/complication in offering a
BaseExceptionGroup(BaseException) in addition to
ExceptionGroup(BaseExceptionGroup, Exception)?
I think the only reason you're comfortable with having to select between
the exceptions that were raised and discard some of them is because that's
where we are today. The PEP lists several standard library and other APIs
that discard errors because they need to pick one. That's what we're trying
to fix.
Irit
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