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ericvsmith commented Sep 24, 2024 •

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Issue: RFE: @dataclasses.dataclass(slots=True) doesn't support methods using zero-arg super() #90562

📚 Documentation preview 📚: https://cpython-previews--124455.org.readthedocs.build/

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ericvsmith added 4 commits

September 23, 2024 20:28


          Fix zero-argument super() for dataclasses with slots=True.

aae4c72


          Use assertIs instead of assertEqual for class comparisons. Add a test…

97d4f31

… showing that the original class, if saved, will have in incorrect __class__ value.


          Fix default role.

c066fe2


          Improved NEWS entry. Tweak some comments.

fbffc50

bedevere-app Bot added the awaiting core review label

Sep 24, 2024

ericvsmith changed the title ~~gt-90562: Support zero argument super with dataclasses when slots=True~~ gh-90562: Support zero argument super with dataclasses when slots=True

Sep 24, 2024

bedevere-app Bot mentioned this pull request

Sep 24, 2024

RFE: @dataclasses.dataclass(slots=True) doesn't support methods using zero-arg super() #90562

Closed


          Merge branch 'main' into issue-90562-dataclasses-zero-argument-super

5e1cc0e

ericvsmith self-assigned this

Sep 24, 2024


          Fix trivial typo in NEWS.

356beed

ericvsmith requested a review from carljm

September 24, 2024 19:25

carljm reviewed

Sep 24, 2024

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Thanks for working on this!

There is the possible case where all methods of a class are decorated with opaque decorators that don't use functools.wraps, and thus we have no route to find the cell to update, and thus this approach simply fails. Should this case be mentioned in the tests? In the docs? Would it be worth explicitly introducing a __classcell__ member on classes through which the cell can reliably be accessed, so as to avoid this problem?

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/dataclasses.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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ericvsmith commented

Sep 24, 2024

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Thanks for the review, @carljm!

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Lib/dataclasses.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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Lib/test/test_dataclasses/__init__.py Resolved

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ericvsmith and others added 2 commits

September 24, 2024 19:38


          Apply suggestions from code review

c801c6d

Apply review suggestions.

Co-authored-by: Carl Meyer <[email protected]>


          Address review comments: Only update one cell, then break out of the …

1c60e6b

…loop; minor change to comments; fix a test.

carljm approved these changes

Sep 24, 2024

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Looks good!

(Discussed in person that if people hit the "all methods use an opaque decorator" case, the answer is "fix the decorator to use functools.wraps")

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bedevere-app Bot added awaiting merge and removed awaiting core review labels

Sep 24, 2024

ericvsmith merged commit 5c6e3b7 into python:main

Sep 25, 2024

bedevere-app Bot removed the awaiting merge label

Sep 25, 2024

ericvsmith deleted the issue-90562-dataclasses-zero-argument-super branch

September 25, 2024 01:26

Bobronium mentioned this pull request

Sep 27, 2024

gh-90562: Improve zero argument support for super() in dataclasses when slots=True #124692

Open

danielhollas mentioned this pull request

Apr 11, 2026

gh-137855: Lazy import inspect module in dataclasses #144387

Merged

gpshead added a commit to gpshead/cpython that referenced this pull request

Apr 12, 2026


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

aa1e00f

…_` and `__delattr__` in frozen dataclasses with slots (pythonGH-144021)

pythongh-105936: Properly update closure cells for `__setattr__` and `__delattr__` in frozen dataclasses with slots (pythonGH-144021)
(cherry picked from commit 8a398bf)

The cherry-pick required additional changes beyond the original commit
because 3.13 lacks the `__class__` closure cell fixup machinery that
was added in 3.14 by pythonGH-124455 (pythongh-90562). Specifically:

- Backported `_update_func_cell_for__class__()` helper function and the
  closure fixup loop in `_add_slots()` from pythonGH-124455. Without these,
  renaming the closure variable from `cls` to `__class__` has no effect
  because nothing updates the cell when the class is recreated with slots.
- Changed `_add_slots()` to use `newcls` instead of reusing `cls` for the
  recreated class, so both old and new class references are available for
  the fixup loop.
- Replaced `assertNotHasAttr` with `assertFalse(hasattr(...))` in tests
  (assertNotHasAttr was added in 3.14).
- Dropped `test_original_class_is_gced` additions (that test does not
  exist on 3.13; it was added by pythonGH-137047 for pythongh-135228 which was not
  backported to 3.13).

Co-authored-by: Prometheus3375 <[email protected]>
Co-authored-by: Sviataslau <[email protected]>
Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

gpshead mentioned this pull request

Apr 12, 2026

[3.13] gh-105936: Properly update closure cells for __setattr__ and __delattr__ in frozen dataclasses with slots (GH-144021) #148476

Merged

gpshead added a commit that referenced this pull request

Apr 26, 2026


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

…_delattr__ in frozen dataclasses with slots (GH-144021) (GH-148476)

gh-105936: Properly update closure cells for `__setattr__` and `__delattr__` in frozen dataclasses with slots (GH-144021)
(cherry picked from commit 8a398bf)

The cherry-pick required additional changes beyond the original commit
because 3.13 lacks the `__class__` closure cell fixup machinery that
was added in 3.14 by GH-124455 (gh-90562). Specifically:

- Backported `_update_func_cell_for__class__()` helper function and the
  closure fixup loop in `_add_slots()` from GH-124455. Without these,
  renaming the closure variable from `cls` to `__class__` has no effect
  because nothing updates the cell when the class is recreated with slots.
- Changed `_add_slots()` to use `newcls` instead of reusing `cls` for the
  recreated class, so both old and new class references are available for
  the fixup loop.
- Replaced `assertNotHasAttr` with `assertFalse(hasattr(...))` in tests
  (assertNotHasAttr was added in 3.14).
- Dropped `test_original_class_is_gced` additions (that test does not
  exist on 3.13; it was added by GH-137047 for gh-135228 which was not
  backported to 3.13).

gh-148947: dataclasses: fix error on empty __class__ cell  (GH-148948)

Also add a test demonstrating the need for the existing "is oldcls" check.
(cherry picked from commit 6d7bbee)

---------

Co-authored-by: Prometheus3375 <[email protected]>
Co-authored-by: Sviataslau <[email protected]>
Co-authored-by: Jelle Zijlstra <[email protected]>
Co-authored-by: Bartosz Sławecki <[email protected]>

hugovk mentioned this pull request

Oct 30, 2026

gh-90562: Fix super() without args calls for dataclasses with slots #111538

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ericvsmith commented Sep 24, 2024 •

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