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JelleZijlstra

opened on Oct 20, 2026

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In the spec, we say (qualifier.rst):

In non-dataclasses, combining ClassVar and Final is redundant, and type checkers may choose to warn or error on the redundancy.

But in the conformance suite we have:

bad9: Final[ClassVar[int]] = 3  # E: ClassVar cannot be nested with Final

(classes_classvar.py)

And:

    VALUE2: ClassVar[Final] = 1  # E: Final cannot be used with ClassVar
    VALUE3: Final[ClassVar] = 1  # E: Final cannot be used with ClassVar

(qualifiers_final_annotation.py)

At runtime, this was an error (if the annotation is evaluated) before 3.12, but it is allowed in 3.13+. We made this runtime change to allow usage in dataclasses.

So the spec makes this an optional error, but the conformance suite requires the error. Most type checkers currently do emit the error, but mypy when targeting 3.13+ allows the nesting (with some bugs: python/mypy#21906).

I would propose to make the errors in the conformance suite optional to match the spec text, but I'd be open to other solutions too.

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1. JelleZijlstra

   added

   topic: otherOther topics not coveredOther topics not covered

   on Oct 20, 2026
2. AlexWaygood commented on Oct 20, 2026

   

   AlexWaygood

   on Oct 20, 2026

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   I believe we added this as a warning-level lint in ty solely so that we would pass this conformance-suite assertion, FWIW
3. davidhalter commented on Oct 21, 2026

   

   davidhalter

   on Oct 21, 2026

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   While I totally agree that #2373 should be merged in case the spec stays this way, I question the sentence:

   In non-dataclasses, combining ClassVar and Final is redundant

   It does not seem the qualifiers in bad9: Final[ClassVar[int]] = 3 are redundant to me. What do I not understand here that everybody else seems to understand?

   The PR that changed this was #1669.
4. JelleZijlstra commented on Oct 21, 2026

   

   JelleZijlstra

   on Oct 21, 2026

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   ClassVar is redundant because a Final object is automatically a ClassVar. What difference do you think there is between:

   class C1:
       attr: Final[ClassVar[int]] = 1
   
   class C2:
       attr: Final[int] = 1
5. davidhalter commented on Oct 21, 2026

   

   davidhalter

   on Oct 21, 2026

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   I guess that makes sense that it's redundant that way, I just thought about this case:

   class C1:
       attr: Final[ClassVar[int]] = 1
   
   class C2:
       attr: ClassVar[int] = 1
   

   where it has different semantics. It feels like the redundancy works only in one direction.

   Reacted by Joren Hammudoglu

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