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Title: gh-143969: Fix frozen+slotted dataclass __setattr__ crash ambiguity by dawdameet · Pull Request #143971 · python/cpython · GitHub

Open Graph Title: gh-143969: Fix frozen+slotted dataclass __setattr__ crash ambiguity by dawdameet · Pull Request #143971 · python/cpython

X Title: gh-143969: Fix frozen+slotted dataclass __setattr__ crash ambiguity by dawdameet · Pull Request #143971 · python/cpython

Description: Fixed Misleading "Not an instance or subtype" error when assigning to property of frozen, slotted dataclass. Fix a crash in frozen dataclasses with slots where the generated setattr and delattr methods used super(cls, self). When slots rebuild the class, the captured cls no longer matches the instance type, causing a TypeError at runtime. Use object.setattr and object.delattr instead to preserve frozen semantics safely. gh-143969

Open Graph Description: Fixed Misleading "Not an instance or subtype" error when assigning to property of frozen, slotted dataclass. Fix a crash in frozen dataclasses with slots where the generated setattr and d...

X Description: Fixed Misleading "Not an instance or subtype" error when assigning to property of frozen, slotted dataclass. Fix a crash in frozen dataclasses with slots where the generated setat...

Opengraph URL: https://github.com/python/cpython/pull/143971

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d3b62e4 gh-143969: Fix frozen+slotted dataclass __setattr__ crash ambiguity dawdameet Jan 17, 2026 https://patch-diff.githubusercontent.com/python/cpython/pull/143971/commits/d3b62e47981e32c4c0463d338ca4529029e3762c
34cfdda gh-143969: Fix crash in frozen slots dataclasses by patching closure … dawdameet Jan 17, 2026 https://patch-diff.githubusercontent.com/python/cpython/pull/143971/commits/34cfddaa82458f6454de0c5f13f5569b50b3088b
9f255ac Update Misc/NEWS.d/next/Library/2026-01-17-23-15-55.gh-issue-143969.W… dawdameet Jan 18, 2026 https://patch-diff.githubusercontent.com/python/cpython/pull/143971/commits/9f255acba06353779ba2a6e234dd8c6a1d9cd281
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