gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible by JelleZijlstra · Pull Request #136893 · python/cpython

JelleZijlstra · Jul 20, 2025

An interesting hack, but more localized in scope than #135230.

This may be a breaking change if people intentionally keep the original class around
when using @dataclass(slots=True), and then use __dict__ or __weakref__ on the
original class.

Issue: 3.14 regression: slot dataclasses classes leak original class #135228

…ke the original class collectible An interesting hack, but more localized in scope than python#135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class.

ncoghlan · Jul 22, 2025

Relying on the __ror__ mapping proxy bypass is unpleasant, but this seems like the simplest near-term workaround, since even though del cls.__weakref__ works without any tricks, del cls.__dict__ fails due to the way that descriptor is defined.

ncoghlan

While far from ideal, this mitigation feels like a better state to leave things in while we ponder the possibilities for a cleaner solution.

Suggested tweaks inline to make it clearer that it's only del cls.__dict__ that needs the mapping proxy bypass.

Lib/dataclasses.py

Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

Lib/dataclasses.py

miss-islington-app · Jul 22, 2025

Thanks @JelleZijlstra for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

…ke the original class collectible (pythonGH-136893) An interesting hack, but more localized in scope than pythonGH-135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. (cherry picked from commit 46cbdf9) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

bedevere-app · Jul 22, 2025

GH-136960 is a backport of this pull request to the 3.14 branch.

…ake the original class collectible (GH-136893) (#136960) gh-135228: When @DataClass(slots=True) replaces a dataclass, make the original class collectible (GH-136893) An interesting hack, but more localized in scope than GH-135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. (cherry picked from commit 46cbdf9) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

…places a dataclass, make the original class collectible (pythonGH-136893) (python#136960)" This reverts commit 6e1b31b. Modifying the `__dict__` is likely to cause crashes

…lass, make the original class collectible (python#136893)" This reverts commit 46cbdf9.

…make the original class collectible (#136893)" (#137014) This reverts commit 46cbdf9.

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

…ke the original class collectible (python#136893) An interesting hack, but more localized in scope than python#135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

* Fix slotted reference cycles on 3.14 Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com> * Add news fragment * Bump version tag to CMA Co-authored-by: Brandt Bucher <40968415+brandtbucher@users.noreply.github.com> Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com> * Apply review comment #1446 (comment) * EAFP --------- Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

…ke the original class collectible (python#136893) An interesting hack, but more localized in scope than python#135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

…lass, make the original class collectible (python#136893)" (python#137014) This reverts commit 46cbdf9.

…ke the original class collectible (python#136893) An interesting hack, but more localized in scope than python#135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

…lass, make the original class collectible (python#136893)" (python#137014) This reverts commit 46cbdf9.

…ass, make the original class collectible (pythonGH-136893) (python#136960) pythongh-135228: When @DataClass(slots=True) replaces a dataclass, make the original class collectible (pythonGH-136893) An interesting hack, but more localized in scope than pythonGH-135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. (cherry picked from commit 46cbdf9) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

JelleZijlstra requested a review from ericvsmith as a code owner July 20, 2025 23:59

bedevere-app bot added the awaiting core review label Jul 20, 2025

bedevere-app bot mentioned this pull request Jul 20, 2025

3.14 regression: slot dataclasses classes leak original class #135228

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ncoghlan approved these changes Jul 22, 2025

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Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

JelleZijlstra added the needs backport to 3.14 bugs and security fixes label Jul 22, 2025

JelleZijlstra commented Jul 22, 2025

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Update Lib/dataclasses.py

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JelleZijlstra merged commit 46cbdf9 into python:main Jul 22, 2025
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bedevere-app bot removed the awaiting merge label Jul 22, 2025

bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Jul 22, 2025

JelleZijlstra deleted the hackweakref branch July 22, 2025 04:51

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 22, 2025

Fix slotted reference cycles on 3.14

cb7dd8f

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

hynek mentioned this pull request Jul 22, 2025

Fix slotted reference cycles on 3.14 python-attrs/attrs#1446

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hynek added a commit to python-attrs/attrs that referenced this pull request Jul 22, 2025

Fix slotted reference cycles on 3.14

d32355b

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

JelleZijlstra mentioned this pull request Jul 22, 2025

[3.14] Revert "[3.14] gh-135228: When @dataclass(slots=True) replaces… #137013

Merged

JelleZijlstra added a commit to JelleZijlstra/cpython that referenced this pull request Jul 22, 2025

Revert "pythongh-135228: When @DataClass(slots=True) replaces a datac…

7a083f3

…lass, make the original class collectible (python#136893)" This reverts commit 46cbdf9.

JelleZijlstra added a commit that referenced this pull request Jul 23, 2025

Revert "gh-135228: When @DataClass(slots=True) replaces a dataclass, …

6a285f9

…make the original class collectible (#136893)" (#137014) This reverts commit 46cbdf9.

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 23, 2025

Fix slotted reference cycles on 3.14

6bb75f8

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

JelleZijlstra mentioned this pull request Jul 23, 2025

gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible (take 2) #137047

Merged

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 25, 2025

Fix slotted reference cycles on 3.14

3ae1bff

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 25, 2025

Fix slotted reference cycles on 3.14

7dd3806

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 27, 2025

Fix slotted reference cycles on 3.14

f4ad208

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

hynek added a commit to python-attrs/attrs that referenced this pull request Jul 27, 2025

Fix slotted reference cycles on 3.14

ea6a62d

Ref python/cpython#136893 & python/cpython#135228 Co-authored-by: Jelle Zijlstra <906600+JelleZijlstra@users.noreply.github.com>

taegyunkim pushed a commit to taegyunkim/cpython that referenced this pull request Aug 4, 2025

Revert "pythongh-135228: When @DataClass(slots=True) replaces a datac…

9df2cfe

…lass, make the original class collectible (python#136893)" (python#137014) This reverts commit 46cbdf9.

Agent-Hellboy pushed a commit to Agent-Hellboy/cpython that referenced this pull request Aug 19, 2025

Revert "pythongh-135228: When @DataClass(slots=True) replaces a datac…

b41a7bd

…lass, make the original class collectible (python#136893)" (python#137014) This reverts commit 46cbdf9.

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gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible#136893

gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible#136893
JelleZijlstra merged 3 commits intopython:mainpython/cpython:mainfrom
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