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

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Merged
merged 3 commits into from
Jul 22, 2025
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gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible #136893

merged 3 commits into from
Jul 22, 2025

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JelleZijlstra
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@JelleZijlstra JelleZijlstra commented Jul 20, 2025 •
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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.

@JelleZijlstra
pythongh-135228: When @DataClass(slots=True) replaces a dataclass, ma…
027f629 
…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.
@bedevere-app bedevere-app bot mentioned this pull request Jul 20, 2025
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@ncoghlan
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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
ncoghlan approved these changes Jul 22, 2025
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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.

@JelleZijlstra @ncoghlan
Apply suggestions from code review
e0d61f7 
Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>
@JelleZijlstra JelleZijlstra added the needs backport to 3.14 bugs and security fixes label Jul 22, 2025
JelleZijlstra
JelleZijlstra commented Jul 22, 2025
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@JelleZijlstra JelleZijlstra merged commit 46cbdf9 into python:main Jul 22, 2025
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Thanks @JelleZijlstra for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Jul 22, 2025
@JelleZijlstra @ncoghlan @miss-islington
pythongh-135228: When @DataClass(slots=True) replaces a dataclass, ma…
c6fde2d 
…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>
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bedevere-app bot commented Jul 22, 2025

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

@bedevere-app bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Jul 22, 2025
@JelleZijlstra JelleZijlstra deleted the hackweakref branch July 22, 2025 04:51
JelleZijlstra added a commit that referenced this pull request Jul 22, 2025
@miss-islington @JelleZijlstra @ncoghlan
[3.14] gh-135228: When @DataClass(slots=True) replaces a dataclass, m…
6e1b31b 
…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>
hynek added a commit to python-attrs/attrs that referenced this pull request Jul 22, 2025
@hynek
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 hynek mentioned this pull request Jul 22, 2025
Open
hynek added a commit to python-attrs/attrs that referenced this pull request Jul 22, 2025
@hynek @JelleZijlstra
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 JelleZijlstra mentioned this pull request Jul 22, 2025
Merged
JelleZijlstra added a commit to JelleZijlstra/cpython that referenced this pull request Jul 22, 2025
@JelleZijlstra
[3.14] Revert "[3.14] pythongh-135228: When @DataClass(slots=True) re…
58b43b2 
…places a dataclass, make the original class collectible (pythonGH-136893) (python#136960)"

This reverts commit 6e1b31b.

Modifying the `__dict__` is likely to cause crashes
JelleZijlstra added a commit to JelleZijlstra/cpython that referenced this pull request Jul 22, 2025
@JelleZijlstra
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
@JelleZijlstra
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
@hynek @JelleZijlstra
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 added a commit to JelleZijlstra/cpython that referenced this pull request Jul 23, 2025
@JelleZijlstra @ncoghlan
pythongh-135228: When @DataClass(slots=True) replaces a dataclass, ma…
916ce1b 
…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>
@JelleZijlstra JelleZijlstra mentioned this pull request Jul 23, 2025
Open
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@ncoghlan ncoghlan ncoghlan approved these changes

@ericvsmith ericvsmith Awaiting requested review from ericvsmith ericvsmith is a code owner

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