False positive: No overload variant of "asdict" matches argument type "Type[DataclassInstance]" [call-overload]
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Description
Bug Report
Mypy 1.11.0 gives me a false positive that 1.10.1 didn't.
Looks like it thinks that is_dataclass() narrows to Type[DataclassInstance], whereas in reality it should probably be something more like Type[DataclassInstance] | DataclassInstance.
Not sure if this is a typeshed issue or a mypy issue, but it might be related to the recent overload changes.
To Reproduce
https://mypy-play.net/?mypy=latest&python=3.8&gist=a561e9787a7710733b09df23d2fc5c04
from dataclasses import dataclass, asdict, is_dataclass
from typing import Any
@dataclass
class Foo:
a: int
foo: Any = Foo(a=1)
if is_dataclass(foo):
asdict(foo)
Expected Behavior
No errors
Actual Behavior
main.py:13: error: No overload variant of "asdict" matches argument type "Type[DataclassInstance]" [call-overload]
main.py:13: note: Possible overload variants:
main.py:13: note: def asdict(obj: DataclassInstance) -> Dict[str, Any]
main.py:13: note: def [_T] asdict(obj: DataclassInstance, *, dict_factory: Callable[[List[Tuple[str, Any]]], _T]) -> _T
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.11.0
- Python version used: 3.8.19
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Run the linked mypy-play reproduction with mypy 1.11.0 and compare its handling of is_dataclass() with the asdict() overloads. Trace the narrowing that produces Type[DataclassInstance] and verify the fix by confirming the example reports no errors.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100