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gh-142214: Fix two regressions in dataclasses #142223

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Merged
JelleZijlstra merged 7 commits into from
Dec 5, 2025
Merged

gh-142214: Fix two regressions in dataclasses #142223

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224f4ad
gh-142214: Fix two regressions in dataclasses
JelleZijlstra Dec 3, 2025
5c3d789
format
JelleZijlstra Dec 3, 2025
42a6898
fix
JelleZijlstra Dec 3, 2025
9a9ef90
fix NEWS syntax
JelleZijlstra Dec 3, 2025
1051d6c
Update Lib/dataclasses.py
JelleZijlstra Dec 3, 2025
320d804
try except
JelleZijlstra Dec 4, 2025
bbbe84d
Merge remote-tracking branch 'upstream/main' into fixdatacl
JelleZijlstra Dec 4, 2025
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14 changes: 10 additions & 4 deletions Lib/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -550,7 +550,12 @@ def __annotate__(format, /):

new_annotations = {}
for k in annotation_fields:
new_annotations[k] = cls_annotations[k]
# gh-142214: The annotation may be missing in unusual dynamic cases.
# If so, just skip it.
try:
new_annotations[k] = cls_annotations[k]
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@ericvsmith ericvsmith Dec 3, 2025

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Don't in and [] both do a lookup? Maybe it would be better as:

if ann := cls_annotations.get(k):
    new_annotations[k] = ann

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@DavidCEllis DavidCEllis Dec 3, 2025

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I believe that None is a valid annotation here so this would miss None values?

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@JelleZijlstra JelleZijlstra Dec 3, 2025

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Correct. To save a lookup we could do a try-except KeyError instead. I don't have a preference but I can switch to that if you like.

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@DavidCEllis DavidCEllis Dec 3, 2025

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I think try/except makes sense as in most cases the key should be there. The key not being there should only be in cases where something has modified annotations and removed things after the class has been processed.

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@JelleZijlstra JelleZijlstra Dec 4, 2025

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Done

except KeyError:
pass

if return_type is not MISSING:
if format == Format.STRING:
Expand Down Expand Up @@ -1399,9 +1404,10 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
f.type = ann

# Fix the class reference in the __annotate__ method
init_annotate = newcls.__init__.__annotate__
if getattr(init_annotate, "__generated_by_dataclasses__", False):
_update_func_cell_for__class__(init_annotate, cls, newcls)
init = newcls.__init__
if init_annotate := getattr(init, "__annotate__", None):
if getattr(init_annotate, "__generated_by_dataclasses__", False):
_update_func_cell_for__class__(init_annotate, cls, newcls)

return newcls

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28 changes: 28 additions & 0 deletions Lib/test/test_dataclasses/__init__.py
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Expand Up @@ -927,6 +927,20 @@ class C:

validate_class(C)

def test_incomplete_annotations(self):
# gh-142214
@dataclass
class C:
"doc" # needed because otherwise we fetch the annotations at the wrong time
x: int

C.__annotate__ = lambda _: {}

self.assertEqual(
annotationlib.get_annotations(C.__init__),
{"return": None}
)

def test_missing_default(self):
# Test that MISSING works the same as a default not being
# specified.
Expand Down Expand Up @@ -2578,6 +2592,20 @@ def __init__(self, x: int) -> None:

self.assertFalse(hasattr(E.__init__.__annotate__, "__generated_by_dataclasses__"))

def test_slots_true_init_false(self):
# Test that slots=True and init=False work together and
# that __annotate__ is not added to __init__.

@dataclass(slots=True, init=False)
class F:
x: int

f = F()
f.x = 10
self.assertEqual(f.x, 10)

self.assertFalse(hasattr(F.__init__, "__annotate__"))

def test_init_false_forwardref(self):
# Test forward references in fields not required for __init__ annotations.

Expand Down
12 changes: 12 additions & 0 deletions Misc/NEWS.d/next/Library/2025-12-03-06-12-39.gh-issue-142214.appYNZ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
Fix two regressions in :mod:`dataclasses` in Python 3.14.1 related to
annotations.

* An exception is no longer raised if ``slots=True`` is used and the
``__init__`` method does not have an ``__annotate__`` attribute
(likely because ``init=False`` was used).

* An exception is no longer raised if annotations are requested on the
``__init__`` method and one of the fields is not present in the class
annotations. This can occur in certain dynamic scenarios.

Patch by Jelle Zijlstra.
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