On 2021-02-23 23:05, Caleb Donovick wrote:
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}`
```
.subgroup returns an ExceptionGroup and .split returns 2 of them.
ExceptionGroup isn't iterable (it's mentioned in the "Rejected Ideas"
section), so your code wouldn't work anyway.
On Mon, Feb 22, 2021 at 4:47 PM Irit Katriel via Python-Dev
<python-dev@python.org <mailto: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/
<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
<https://github.com/iritkatriel/cpython/pull/10>
Thank you for your help
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