Description

assignee = 'https://github.com/ericvsmith'
closed_at = None
created_at = <Date 2022-03-10.00:14:28.417>
labels = ['type-bug', 'library', '3.10']
title = 'dataclass(slots=True) incompatible with __init_subclass__'
updated_at = <Date 2022-03-10.00:28:03.767>
user = 'https://github.com/crusaderky'

activity = <Date 2022-03-10.00:28:03.767>
actor = 'eric.smith'
assignee = 'eric.smith'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-03-10.00:14:28.417>
creator = 'crusaderky'
dependencies = []
files = []
hgrepos = []
issue_num = 46970
keywords = []
message_count = 2.0
messages = ['414822', '414823']
nosy_count = 2.0
nosy_names = ['eric.smith', 'crusaderky']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46970'
versions = ['Python 3.10']

Activity

1. crusaderky commented on Mar 10, 2022

   

   crusaderkymannequin

   on Mar 10, 2022

   MannequinAuthor

   More actions

   Related to bpo-46382
   A class decorated with dataclass(slots=True) can't pass any parameters to the __init_subclass__ method of its parent class.

   from dataclasses import dataclass
   
   class A:
       __slots__ = ()
       def __init_subclass__(cls, msg):
           print(msg)
   
   @dataclass(slots=True)
   class B(A, msg="Hello world!"):
       pass

   File "lib/python3.10/dataclasses.py", line 1145, in _add_slots
   cls = type(cls)(cls.__name__, cls.__bases__, cls_dict)
   TypeError: A.__init_subclass__() missing 1 required positional argument: 'msg'
2. crusaderky

   added

   3.10 (EOL)end of lifeend of life

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

   on Mar 10, 2022
3. ericvsmith commented on Mar 10, 2022

   

   ericvsmith

   on Mar 10, 2022

   Member

   More actions

   This appears to be due to dataclasses needing to create a new class in order to set __slots__. I'll look at it, but I doubt there's anything that can be done.

   attrs has the same issue:
   File "xxxxx/.local/lib/python3.8/site-packages/attr/make.py", line 889, in _create_slots_class
   cls = type(self._cls)(self._cls.__name_, self._cls.__bases__, cd)
   TypeError: __init_subclass__() missing 1 required positional argument: 'msg'
4. ericvsmith

   self-assigned this

   on Mar 10, 2022
5. ericvsmith

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   and removed

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

   on Mar 10, 2022
6. ericvsmith

   self-assigned this

   on Mar 10, 2022
7. ericvsmith

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   and removed

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

   on Mar 10, 2022
8. ezio-melotti

   transferred this issue fromon Apr 10, 2022
9. andreabak

   added a commit that references this issue on Aug 27, 2023

   fix: make compatible with python3.10

   fcb59c9
10. picnixz

    added

    topic-dataclasses

    on Aug 16, 2024
11. sobolevn commented on Aug 23, 2024

    

    sobolevn

    on Aug 23, 2024

    Member

    More actions

    I think that we should add this case to the docs. Because there's really nothing we can do to support this case.

    Solutions:

    1. Don't do that
    2. Don't use slots=True, write manual slots
    3. Have defaults for __init_subclass__

    I will send a PR with the proposed note about that.
12. sobolevn

    self-assigned this

    on Aug 23, 2024
13. sobolevn

    added 2 commits that reference this issue on Aug 26, 2024

    pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…

    0939d82

    gh-91126: Docs and tests for slotted dataclasses with `__init_subclas…

    75e7282
14. miss-islington

    added 2 commits that reference this issue on Sep 1, 2024

    pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…

    9265957

    pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…

    33a044b
15. sobolevn

    added 2 commits that reference this issue on Sep 1, 2024

    [3.12] gh-91126: Docs and tests for slotted dataclasses with `__init_…

    12db938

    [3.13] gh-91126: Docs and tests for slotted dataclasses with `__init_…

    cfdf376
16. sobolevn

    closed this as completedon Sep 1, 2024

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