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The resolution for #137530, #137711 which was backported to 3.14 and included in 3.14.1, breaks dataclasses without __init__.
Although a dataclass without __init__ doesn't seem that helpful, it doesn't seem to be explicitly forbidden and shouldn't break in a point release.

from dataclasses import dataclass, field

@dataclass(slots=True, init=False)
class MyClass:
    attr: int

    def __new__(cls, attr: int) -> Self:
        self.attr = attr
        return self

Error message:

$ python3 dataclasses_issue.py
Traceback (most recent call last):
  File "/home/erik/dataclasses_issue.py", line 3, in <module>
    @dataclass(slots=True, init=False)
     ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/erik/.pyenv/versions/3.14.1/lib/python3.14/dataclasses.py", line 1426, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
                          frozen, match_args, kw_only, slots,
                          weakref_slot)
  File "/home/erik/.pyenv/versions/3.14.1/lib/python3.14/dataclasses.py", line 1234, in _process_class
    cls = _add_slots(cls, frozen, weakref_slot, fields)
  File "/home/erik/.pyenv/versions/3.14.1/lib/python3.14/dataclasses.py", line 1401, in _add_slots
    init_annotate = newcls.__init__.__annotate__
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'wrapper_descriptor' object has no attribute '__annotate__'. Did you mean: '__getstate__'?

CPython versions tested on:

3.14.1

Operating systems tested on:

Linux

Linked PRs

Reacted by Giulio Mazzanti, Robert Resch, SamWarden, Bas Nijholt, ADBond, Oleksandr Kravets, Barak Ugav, Radomir Stevanovic, Alex Kennedy, Alfredo Luque and 6 more

Activity

emontnemery
added
type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error
on Dec 3, 2025
emontnemery
changed the title ~~[-]Dataclasses without __init__ no longer work due to #137711[/-]~~ [+]Dataclasses without __init__ no longer work in 3.14.1 due to #137711[/+] on Dec 3, 2025

dpinol commented on Dec 3, 2025

dpinol

on Dec 3, 2025

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as an example, it breaks networkx 3.6

  File "/usr/local/lib/python3.14/site-packages/networkx/utils/configs.py", line 8, in <module>
    @dataclass(init=False, eq=False, slots=True, kw_only=True, match_args=False)
     ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.14/dataclasses.py", line 1426, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
                          frozen, match_args, kw_only, slots,
                          weakref_slot)
  File "/usr/local/lib/python3.14/dataclasses.py", line 1234, in _process_class
    cls = _add_slots(cls, frozen, weakref_slot, fields)
  File "/usr/local/lib/python3.14/dataclasses.py", line 1401, in _add_slots
    init_annotate = newcls.__init__.__annotate__
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'wrapper_descriptor' object has no attribute '__annotate__'. Did you mean: '__getstate__'?

Reacted by Vladimir Vargas-Calderón, clayote, Oleksandr Kravets, Barak Ugav, Wim Jeantine-Glenn, Aryazaky and Lenormand Julien

Reacted by Ross Barnowski and Oleksandr Kravets

Giuzzilla commented on Dec 3, 2025

Giuzzilla

on Dec 3, 2025

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Python 3.14.1 is breaking my sqlalchemy-based project as well, seems related to the issue/dataclasses, stacktrace:

mypackage/mymodel.py:109: in <module>
    class MyModel(Base, kw_only=True):
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_api.py:626: in __init_subclass__
    super().__init_subclass__(**kw)
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_api.py:846: in __init_subclass__
    _as_declarative(cls._sa_registry, cls, cls.__dict__)
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_base.py:245: in _as_declarative
    return _MapperConfig.setup_mapping(registry, cls, dict_, None, {})
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_base.py:326: in setup_mapping
    return _ClassScanMapperConfig(
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_base.py:564: in __init__
    self._setup_dataclasses_transforms()
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_base.py:1171: in _setup_dataclasses_transforms
    self._apply_dataclasses_to_any_class(
.venv/lib/python3.14/site-packages/sqlalchemy/orm/decl_base.py:1227: in _apply_dataclasses_to_any_class
    dataclass_callable(  # type: ignore[call-overload]
/usr/local/lib/python3.14/dataclasses.py:1436: in dataclass
    return wrap(cls)
           ^^^^^^^^^
/usr/local/lib/python3.14/dataclasses.py:1426: in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
/usr/local/lib/python3.14/dataclasses.py:1217: in _process_class
    text_sig = str(inspect.signature(
/usr/local/lib/python3.14/inspect.py:3321: in signature
    return Signature.from_callable(obj, follow_wrapped=follow_wrapped,
/usr/local/lib/python3.14/inspect.py:3036: in from_callable
    return _signature_from_callable(obj, sigcls=cls,
/usr/local/lib/python3.14/inspect.py:2557: in _signature_from_callable
    return _get_signature_of(init)
           ^^^^^^^^^^^^^^^^^^^^^^^
/usr/local/lib/python3.14/inspect.py:2440: in _signature_from_callable
    sig = _get_signature_of(obj.__func__)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/local/lib/python3.14/inspect.py:2511: in _signature_from_callable
    return _signature_from_function(sigcls, obj,
/usr/local/lib/python3.14/inspect.py:2334: in _signature_from_function
    annotations = get_annotations(func, globals=globals, locals=locals, eval_str=eval_str,
/usr/local/lib/python3.14/annotationlib.py:973: in get_annotations
    ann = _get_and_call_annotate(obj, format)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/local/lib/python3.14/annotationlib.py:1112: in _get_and_call_annotate
    ann = call_annotate_function(annotate, format, owner=obj)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/local/lib/python3.14/annotationlib.py:711: in call_annotate_function
    return annotate(format)
           ^^^^^^^^^^^^^^^^
/usr/local/lib/python3.14/dataclasses.py:553: in __annotate__
    new_annotations[k] = cls_annotations[k]
                         ^^^^^^^^^^^^^^^^^^
E   KeyError: 'my_field'

pareshjoshij commented on Dec 3, 2025
pareshjoshij
on Dec 3, 2025
Contributor
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Looks like we're seeing two different side effects from the recent annotation updates.

1 The NetworkX crash: It seems init=False exposes object.init (a wrapper descriptor), which naturally lacks annotate.

2 The SQLAlchemy KeyError: It looks like the code assumes every field must exist in cls_annotations. That assumption might be too strict for dynamic classes where attributes are injected.

I suspect adding guards in both spots to handle missing attributes/keys would fix this?
sobolevn commented on Dec 3, 2025
sobolevn
on Dec 3, 2025
Member
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Also got this error today: https://github.com/wemake-services/django-modern-rest/actions/runs/19889091191/job/57003155723
sobolevn
added
topic-typing

topic-dataclasses
on Dec 3, 2025
pareshjoshij commented on Dec 3, 2025
pareshjoshij
on Dec 3, 2025
Contributor
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@epenet that link speaks volumes.

The fact that they had to rush that merge to unblock CI—even skipping the documentation steps you suggested—really confirms how severe the instability is for downstream users.
terryjreedy
changed the title ~~[-]Dataclasses without __init__ no longer work in 3.14.1 due to #137711[/-]~~ [+]Dataclasses without `__init__` no longer work in 3.14.1 due to #137711[/+] on Dec 3, 2025
picnixz
added
stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

3.14bugs and security fixesbugs and security fixes

3.15bugs and security fixesbugs and security fixes

release-blocker
on Dec 3, 2025
github-project-automation
added this to Release and Deferred blockers 🚫on Dec 3, 2025
20 remaining items
ewels
added a commit that references this issue on Dec 5, 2025
Avoid Python 3.14.1
bd01d4f
hugovk commented on Dec 5, 2025
hugovk
on Dec 5, 2025
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Thanks all, merged and backported, will hopefully be released in 3.14.2 today.
Reacted by David Ellis, Chenxin Zhong, Jens Tonberg Larsson, Alex Kennedy, Yz, Ross Barnowski and robinechuca
Reacted by Alex Waygood, Chenxin Zhong, Srinivas Gorur-Shandilya, Jens Tonberg Larsson, Ross Barnowski and ADBond
hugovk
closed this as completed on Dec 5, 2025
github-project-automation
moved this from Todo to Done in Release and Deferred blockers 🚫on Dec 5, 2025
rossbar
added a commit that references this issue on Dec 5, 2025
DEP: blocklist 3.14.1
973d5ed
StanFromIreland
added a commit that references this issue on Dec 6, 2025
pythongh-142214: Fix two regressions in dataclasses (python#142223)
3265f88
MridulS
added a commit that references this issue on Dec 7, 2025
Blocklist Python 3.14.1 (#8372)
c38830c
fedarko
added a commit that references this issue on Dec 8, 2025
Add Python 3.14 back to CI matrix
b67c275
wimglenn commented on Dec 10, 2025
wimglenn
on Dec 10, 2025
Contributor
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I was thinking, could there be something in the CPython release process for maintenance releases which sanity checks that an assortment of heavily used libraries such as networkx and sqlalchemy can successfully import?

That sounds like some low hanging fruit, and something easy to automate for catching potentially disruptive issues before the release is published and gets picked up by various GitHub actions. I had some uv python install 3.14 in .github/workflows which automatically picked up the micro bump on Dec 2 and CIs got trashed (fortunately the fix was trivial just pinning it to 3.14.0 in the workflow yaml).
hugovk commented on Dec 10, 2025
hugovk
on Dec 10, 2025
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It's been considered in the past (for example, PEP 608 / https://discuss.python.org/t/rejected-rfc-pep-608-coordinated-python-release/2539 six years ago) but iirc rejected due to the amount of work and diversity of test setups.

I suggest opening a new discussion, though, if you think things are better now to retry it.
Reacted by Victor Stinner
zzzeek commented on Dec 10, 2025
zzzeek
on Dec 10, 2025
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a coordinated release seems a little heavy handed, but there's no reason people (anyone, python devs, OSS authors, interested parties) can't run CIs (like a series of github actions somehwere) that test the Python main branch against some series of OSS libraries, and just report github issues for failures that are observed.

CIs like these can be burdensome as when you are tracking the "main" of another project, there's often unrelated problems that get checked into main. plus you have to stay on top of deployment / test runner changes in the project (though cPython is extremely good at staying exactly the same in my experience).
encukou commented on Dec 10, 2025
encukou
on Dec 10, 2025
Member
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I've been thinking whether the 3.x.1 release needs a RC period, given that all fixes from the long 3.x.0 RC period land there.
Reacted by Itamar Oren
alexlancaster
added 2 commits that reference this issue on Dec 11, 2025
conditionally pin macos builds to 3.14.0
07b2178
Temporary pin of Python 3.14.0 to work around upstream bug (#113)
24c0b10
hugovk commented on Feb 2, 2026
hugovk
on Feb 2, 2026
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Reported @stomde to GitHub.
Reacted by Alex Waygood

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GeezerVison

Dataclasses without __init__ no longer work in 3.14.1 due to #137711 #142214

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

dpinol commented on Dec 3, 2025

Giuzzilla commented on Dec 3, 2025

pareshjoshij commented on Dec 3, 2025

sobolevn commented on Dec 3, 2025

pareshjoshij commented on Dec 3, 2025

20 remaining items

hugovk commented on Dec 5, 2025

wimglenn commented on Dec 10, 2025

hugovk commented on Dec 10, 2025

zzzeek commented on Dec 10, 2025

encukou commented on Dec 10, 2025

hugovk commented on Feb 2, 2026

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Dataclasses without `init` no longer work in 3.14.1 due to #137711 #142214