[issue46967] Type union for except

[Irit Katriel]

Irit Katriel  added the comment:

> I don't think that `except A|B` looks better than `except (A, B)`

I agree.

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resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue46967] Type union for except

[Guido van Rossum]

Guido van Rossum  added the comment:

I don't think that `except A|B` looks better than `except (A, B)`, so I am 
against this proposal. Exception matching is its own special thing (e.g. it 
doesn't honor virtual subclasses) and we shouldn't hyper-generalize.

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[issue46967] Type union for except

[Steven D'Aprano]

Change by Steven D'Aprano :


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nosy: +steven.daprano

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[issue46967] Type union for except

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:

This would be nice but I'm not sure it's worth the hassle in terms of 
documentation, tooling support, etc.

There is an existing issue (that I can't find right now) that makes the 
`except` machinery use `__instancecheck__`, instead of looking only at real 
base classes like it does now. That change would automatically also make `|` 
work.

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[issue46967] Type union for except

[Alex Waygood]

Change by Alex Waygood :


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nosy: +AlexWaygood, Jelle Zijlstra, gvanrossum, iritkatriel

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[issue46967] Type union for except

[Henry Schreiner]

New submission from Henry Schreiner :

In 3.10 via PEP 604, there was an attempt to use the new union of types where 
runtime types were previously expected to be a tuple. `isinstance(x, (A, B))` 
can be written `isinstance(x, A | B)`. Unfortunately, there still is a case 
were a tuple of types is required: `except (A, B) as err:` cannot be written 
`except A | B as err:`. I think this should be allowed; it is consistent with 
isinstance and pattern matching's use of |, and nicely avoids confusion with 
`except A, B:` which is disallowed for Python 2 reasons; `except A | B`: would 
be valid.

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components: Interpreter Core
messages: 414807
nosy: Henry Schreiner
priority: normal
severity: normal
status: open
title: Type union for except
type: enhancement
versions: Python 3.11

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