dataclass(slots=True) incompatible with __init_subclass__

[crusaderky]

BPO	46970
Nosy	@ericvsmith, @crusaderky

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

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'

bugs.python.org fields:

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']

Linked PRs

• gh-91126: Docs and tests for slotted dataclasses with __init_subclass__ #123342
• [3.13] gh-91126: Docs and tests for slotted dataclasses with __init_subclass__ (GH-123342) #123568
• [3.12] gh-91126: Docs and tests for slotted dataclasses with __init_subclass__ (GH-123342) #123569

[crusaderky]

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'