What is the motivation for returning `None` on empty splits? I feel like
this creates an unnecessary asymmetry. I don't personally have a use
case for the this feature so I may be missing something but it seems like
it would force an annoying pattern:
```
try:
foo()
except ExceptionGroup as eg:
g1, g2 = eg.split(predicate)
for e in g1:
handle_true(e)
for e in g2:
handle_false(e)
```
Would need to be written:
```
try:
foo()
except ExceptionGroup as eg:
g1, g2 = eg.split(predicate)
if g1 is not None:
for e in g1:
handle_true(e)
if g2 is not None:
for e in g2:
handle_false(e)
```
Also this creates an subtle difference with subgroup:
```
g1, g2 = eg.split(predicate)
h1, h2 = eg.subgroup(predicate), eg.subgroup(lambda e: not predicate(e))
assert g1 == h1 and g2 == h2 # only true if `None not in {g1, g2}`
```
On Mon, Feb 22, 2021 at 4:47 PM Irit Katriel via Python-Dev <
python-dev@python.org> wrote:
>
> Hi all,
>
> We would like to request feedback on PEP 654 -- Exception Groups and
> except*.
>
> https://www.python.org/dev/peps/pep-0654/
>
> It proposes language extensions that allow programs to raise and handle
> multiple unrelated
> exceptions simultaneously, motivated by the needs of asyncio and other
> concurrency libraries,
> but with other use cases as well.
>
> * A new standard exception type, ExceptionGroup, to represent multiple
> exceptions with
> shared traceback.
> * Updates to the traceback printing code to display (possibly nested)
> ExceptionGroups.
> * A new syntax except* for handling ExceptionGroups.
>
> A reference implementation (unreviewed) can be found at:
> https://github.com/iritkatriel/cpython/pull/10
>
> Thank you for your help
>
> Kind regards
> Irit, Yury & Guido
>
>
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