PEP-681 - Inheriting class doesn't recognize kw_only=True from parent class
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Description
Bug Report
A class inheriting a class with kw_only=True and using a dataclass_transform doesn't recognize kw_only being set, even though in runtime it does not yield an error. Originally found in sqlalchemy's usage (https://github.com/sqlalchemy/sqlalchemy/issues/11485)
To Reproduce
from typing import Optional, Any
import typing_extensions
def field(default: Any=None, init: bool=True, repr: bool=True) -> Any:
pass
@typing_extensions.dataclass_transform(
field_specifiers=(
field,
)
)
class ModelMeta(type):
pass
class ModelBase(metaclass=ModelMeta):
def __init_subclass__(cls, kw_only: bool=False) -> None:
pass
class Base(ModelBase, kw_only=True):
pass
class Vehicle(Base):
b: Optional[str] = field(default=None)
c: int
Expected Behavior
No error.
Actual Behavior
error: Attributes without a default cannot follow attributes with one [misc]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.10
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.12
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the minimal Python reproducer in the issue and trace mypy's PEP 681 dataclass_transform handling for inherited kw_only settings. Compare the reported ordering error with the expected behavior, then add a regression test for this reproducer and run the relevant test suite to confirm that no error is reported.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100