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(🎁) Intersections with @final types should trigger unreachable errors #15148

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KotlinIsland opened this issue Apr 26, 2023 · 2 comments · Fixed by #16330
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(🎁) Intersections with @final types should trigger unreachable errors #15148

KotlinIsland opened this issue Apr 26, 2023 · 2 comments · Fixed by #16330
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feature topic-final PEP 591 topic-reachability Detecting unreachable code

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@KotlinIsland
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KotlinIsland commented Apr 26, 2023 •
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from typing import final

@final
class A: ...
class B: ...

a: A
assert isinstance(a, B)
reveal_type(a)  # note: Revealed type is "__main__.<subclass of "A" and "B">"
print("hi") # no unreachable error
@KotlinIsland KotlinIsland mentioned this issue Apr 26, 2023
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@erictraut erictraut mentioned this issue Apr 27, 2023
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@AlexWaygood AlexWaygood added topic-reachability Detecting unreachable code topic-final PEP 591 labels Apr 28, 2023
@NeilGirdhar
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NeilGirdhar commented May 1, 2023 •
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"Intersections with @final types should trigger unreachable errors"… (unless A already inherits from B of course 😄)

This was referenced Oct 25, 2023
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@tyralla
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tyralla commented Oct 27, 2023

@KotlinIsland: #16330 should fix this issue. Would you like to review it?

hauntsaninja pushed a commit that referenced this issue Dec 4, 2023
@tyralla
Do not intersect types in isinstance checks if at least one is final (#…
c224da5 
…16330)

Fixes #15148

I think it also fixes the [initial
bug](#12163 (comment))
reported in #12163 (this is why I added a TypeVar test case) but not
[this
bug](#12163 (comment))
reported later in the same issue.
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feature topic-final PEP 591 topic-reachability Detecting unreachable code
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Do not intersect types in isinstance checks if at least one is final. tyralla/mypy
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@NeilGirdhar @tyralla @KotlinIsland @AlexWaygood