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[question] dictionary _KT typevar and hashability #3884

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BvB93 opened this issue Mar 27, 2020 · 3 comments
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[question] dictionary _KT typevar and hashability #3884

BvB93 opened this issue Mar 27, 2020 · 3 comments

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@BvB93
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BvB93 commented Mar 27, 2020

Dear all,

I recently noticed that the _KT typevar used in annotating dict has no upper bound specified, yet dictionary keys must (as far as I'm aware) always be hashable.

Is there a reason here as to why _KT is not defined as TypeVar('_KT', bound=Hashable)?

Regards, Bas
@JelleZijlstra
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The Hashable type can't really be typechecked (because all types are hashable by default); see prior discussion in #2148, python/mypy#1746, python/mypy#2455.

@BvB93
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BvB93 commented Apr 4, 2020

Thanks for the info!
I'd consider this question answered.

@BvB93 BvB93 closed this as completed Apr 4, 2020
@hauntsaninja hauntsaninja mentioned this issue Apr 25, 2020
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@ikonst
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ikonst commented Apr 26, 2020

Given that certain types are marked as non-hashable (#3219) wouldn't this have at least a fringe value?

This was referenced Nov 5, 2021
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MaxG87 added a commit to MaxG87/collectiondict that referenced this issue Mar 20, 2024
@MaxG87
test: Add test that should be a type error
ae4f776 
It would be best if `mypy` would directly reject unhashable types, but
according to python/typeshed#3884 this is
unfeasible. Therefore, a small tests is added to serve as marker and
playground.
MaxG87 added a commit to MaxG87/collectiondict that referenced this issue Mar 20, 2024
@MaxG87
test: Add test that should be a type error
4fb40cf 
It would be best if `mypy` would directly reject unhashable types, but
according to python/typeshed#3884 this is
unfeasible. Therefore, a small tests is added to serve as marker and
playground.
MaxG87 added a commit to MaxG87/collectiondict that referenced this issue Mar 20, 2024
@MaxG87
test: Add test that should be a type error
0149ecb 
It would be best if `mypy` would directly reject unhashable types, but
according to python/typeshed#3884 this is
unfeasible. Therefore, a small tests is added to serve as marker and
playground.
MaxG87 added a commit to MaxG87/collectiondict that referenced this issue Mar 20, 2024
@MaxG87
test: Add test that should be a type error
c9dadf9 
It would be best if `mypy` would directly reject unhashable types, but
according to python/typeshed#3884 this is
unfeasible. Therefore, a small tests is added to serve as marker and
playground.
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3 participants
@JelleZijlstra @ikonst @BvB93