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dataclasses: frozen dataclasses with slots' __setattr__ and __delattr__ does not work. #105936

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dataclasses: frozen dataclasses with slots' __setattr__ and __delattr__ does not work.#105936
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gpshead
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stdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@avboag
avboag
opened on Jun 20, 2023

Bug report

The check in frozen dataclasses' __setattr__ and __delattr__ does not work when slots=True:

@dataclass(frozen=True, slots=True)
class C:
    i: int

C(10).j = 5

crashes with

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 5, in __setattr__
TypeError: super(type, obj): obj must be an instance or subtype of type

instead of raising a FrozenInstanceError.

Likewise,

@dataclass(frozen=True, slots=True)
class C:
    i: int

class D(C):
    pass

D(10).j = 5

crashes with the same error instead of working.

Linked PRs

Activity

  1. avboag
    added
    type-bugAn unexpected behavior, bug, or error
    on Jun 20, 2023
  2. iritkatriel
    added
    stdlibStandard Library Python modules in the Lib/ directory
    on Nov 26, 2023
  3. gpshead
    added a commit that references this issue on Apr 12, 2026

    gh-105936: Properly update closure cells for `__setattr__` and `__del…

    8a398bf
  4. miss-islington
    added a commit that references this issue on Apr 12, 2026

    pythongh-105936: Properly update closure cells for `__setattr__` and …

    3fcd711
  5. gpshead
    added 3 commits that reference this issue on Apr 12, 2026

    pythongh-105936: Properly update closure cells for `__setattr__` and …

    6645d06

    [3.14] gh-105936: Properly update closure cells for `__setattr__` and…

    942d302

    [3.13] pythongh-105936: Properly update closure cells for `__setattr_…

    aa1e00f

  6. gpshead commented on Apr 13, 2026

    @gpshead
    gpshead
    on Apr 13, 2026
    Member

    A 3.13 is up as a Draft PR because it requires more changes and backporting pieces of some other stuff that is already in 3.14 in order for it to work.

  7. prakashsellathurai
    added a commit that references this issue on Apr 13, 2026

    Revert "pythongh-105936: Properly update closure cells for `__setattr…

    cdcefcb
  8. ljfp
    added a commit that references this issue on Apr 25, 2026

    pythongh-105936: Properly update closure cells for `__setattr__` and …

    187221c
  9. gpshead
    added a commit that references this issue on Apr 26, 2026

    [3.13] gh-105936: Properly update closure cells for __setattr__ and _…

    9651429
  10. gpshead
    self-assigned this
    on Apr 26, 2026

  11. gpshead commented on Apr 26, 2026

    @gpshead
    gpshead
    on Apr 26, 2026
    Member

    all merged. thanks for the report, contributions and reviews.

  12. gpshead
    closed this as completedon Apr 26, 2026
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stdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

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