8000 dataclass(slots=True) incompatible with __init_subclass__ · Issue #91126 · python/cpython · GitHub
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crusaderky mannequin opened this issue Mar 10, 2022 · 3 comments
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dataclass(slots=True) incompatible with __init_subclass__ #91126

crusaderky mannequin opened this issue Mar 10, 2022 · 3 comments
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@ericvsmith @sobolevn
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3.10 only security fixes stdlib Python modules in the Lib dir topic-dataclasses type-bug An unexpected behavior, bug, or error

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@crusaderky
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crusaderky mannequin commented Mar 10, 2022 •
edited by bedevere-app bot
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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']

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@crusaderky
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crusaderky mannequin commented Mar 10, 2022

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'

@crusaderky crusaderky mannequin added 3.10 only security fixes stdlib Python modules in the Lib dir type-crash A hard crash of the interpreter, possibly with a core dump labels Mar 10, 2022
@ericvsmith
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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'

@ericvsmith ericvsmith self-assigned this Mar 10, 2022
@ericvsmith ericvsmith added type-bug An unexpected behavior, bug, or error and removed type-crash A hard crash of the interpreter, possibly with a core dump labels Mar 10, 2022
@ericvsmith ericvsmith self-assigned this Mar 10, 2022
@ericvsmith ericvsmith added type-bug An unexpected behavior, bug, or error and removed type-crash A hard crash of the interpreter, possibly with a core dump labels Mar 10, 2022
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
andreabak added a commit to andreabak/sibilant that referenced this issue Aug 27, 2023
@andreabak
fix: make compatible with python3.10
fcb59c9 
The main change is to remove slots=True from dataclasses decorators,
due to CPython bug: python/cpython#91126
@sobolevn
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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.

@sobolevn sobolevn self-assigned this Aug 23, 2024
sobolevn added a commit to sobolevn/cpython that referenced this issue Aug 26, 2024
@sobolevn
pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…
0939d82 
…ubclass__`
@bedevere-app bedevere-app bot mentioned this issue Aug 26, 2024
Merged
sobolevn added a commit that referenced this issue Sep 1, 2024
@sobolevn
gh-91126: Docs and tests for slotted dataclasses with `__init_subclas…
75e7282 
…s__` (#123342)
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Sep 1, 2024
@sobolevn @miss-islington
pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…
9265957 
…ubclass__` (pythonGH-123342)

(cherry picked from commit 75e7282)

Co-authored-by: sobolevn <mail@sobolevn.me>
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Sep 1, 2024
@sobolevn @miss-islington
pythongh-91126: Docs and tests for slotted dataclasses with `__init_s…
33a044b 
…ubclass__` (pythonGH-123342)

(cherry picked from commit 75e7282)

Co-authored-by: sobolevn <mail@sobolevn.me>
This was referenced Sep 1, 2024
Merged
Merged
sobolevn added a commit that referenced this issue Sep 1, 2024
@miss-islington @sobolevn
[3.12] gh-91126: Docs and tests for slotted dataclasses with `__init_…
12db938 
…subclass__` (GH-123342) (#123569)

gh-91126: Docs and tests for slotted dataclasses with `__init_subclass__` (GH-123342)
(cherry picked from commit 75e7282)

Co-authored-by: sobolevn <mail@sobolevn.me>
sobolevn added a commit that referenced this issue Sep 1, 2024
@miss-islington @sobolevn
[3.13] gh-91126: Docs and tests for slotted dataclasses with `__init_…
cfdf376 
…subclass__` (GH-123342) (#123568)

gh-91126: Docs and tests for slotted dataclasses with `__init_subclass__` (GH-123342)
(cherry picked from commit 75e7282)

Co-authored-by: sobolevn <mail@sobolevn.me>
@sobolevn sobolevn closed this as completed Sep 1, 2024
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@sobolevn sobolevn

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3.10 only security fixes stdlib Python modules in the Lib dir topic-dataclasses type-bug An unexpected behavior, bug, or error
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