can't specify generic types when instantiating frozen dataclass with slots

Bug report

Bug description:

from dataclasses import dataclass

@dataclass(frozen=True, slots=True)
class Foo[T]:
  pass

foo = Foo() # this line works
foo = Foo[int]() # this one does not

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.12/typing.py", line 1142, in __call__
    result.__orig_class__ = self
    ^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 5, in __setattr__
TypeError: super(type, obj): obj must be an instance or subtype of type

Python 3.12.2 (main, Feb 21 2024, 00:00:00) [GCC 13.2.1 20231205 (Red Hat 13.2.1-6)]

CPython versions tested on:

3.12

Operating systems tested on:

Linux

FYI: this doesn't relate to the new (PEP 695) syntax.
Example with the old syntax:

from dataclasses import dataclass
from typing import TypeVar, Generic


T = TypeVar("T")


@dataclass(frozen=True, slots=True)
class Foo(Generic[T]):
  pass

foo = Foo() # this line works
foo = Foo[int]() # this one does not

Traceback (most recent call last):
  File "/home/eclips4/CLionProjects/cpython/example.py", line 13, in <module>
    foo = Foo[int]() # this one does not
          ^^^^^^^^^^
  File "/usr/local/lib/python3.11/typing.py", line 1277, in __call__
    result.__orig_class__ = self
    ^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 5, in __setattr__
TypeError: super(type, obj): obj must be an instance or subtype of type

Happily, this specific exception was fixed just last month, in #115213. The fix was backported, so it will be included in the next releases of Python 3.12 and Python 3.11. The typing module is in the clear here.

However, it looks like dataclasses might also be using super() incorrectly there? Not sure.

@ericvsmith

This is a symptom of the general problem where slotted dataclasses work by creating a new class, which breaks super(). There are several other similar issues and there's no obvious solution.

cc @ericvsmith for dataclasses.

@ericvsmith

This is a symptom of the general problem where slotted dataclasses work by creating a new class, which breaks super(). There are several other similar issues and there's no obvious solution.

cc @ericvsmith for dataclasses.

If there are already other similar issues regarding super() in dataclasses, then we can probably close this one, as the user-visible bug here has already been fixed by #115213

https://github.com/python/cpython/issues?q=is%3Aissue+is%3Aopen+dataclasses+slots+super lists several.

@daddinuz

Thanks for the report, @daddinuz! Your bug was valid; we'd just already fixed it before you filed the issue ;)

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can't specify generic types when instantiating frozen dataclass with slots #116669

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can't specify generic types when instantiating frozen dataclass with slots #116669

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

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Eclips4 commented on Mar 12, 2024

AlexWaygood commented on Mar 12, 2024

Eclips4 commented on Mar 12, 2024

JelleZijlstra commented on Mar 12, 2024

AlexWaygood commented on Mar 12, 2024

JelleZijlstra commented on Mar 12, 2024

AlexWaygood commented on Mar 12, 2024

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