Type of generic property subclass reveals <nothing>
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Description
Bug Report
When subclassing property and returning a generic type, mypy reveals <nothing> as the type of the property.
Pyright reveals the expected type.
To Reproduce
from typing import Any, Generic, Optional, Type, TypeVar
T = TypeVar("T")
class customProperty(property, Generic[T]):
def __get__(self, obj: Any, owner: Optional[Type] = None) -> T:
return super().__get__(obj, owner)
class C:
@customProperty
def prop(self) -> int:
return 1
reveal_type(C().prop)
Expected Behavior
Revealed type is "builtins.int"
Actual Behavior
Revealed type is "<nothing>"
Your Environment
- Mypy version used: 0.950
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.10
- Operating system and version: Ubuntu 22.04
Pyright 1.1.244 however seems to get it right and returns the expected type
Type of "C().prop" is "int"
This could be related to #11115
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 by running the provided Python reproduction with mypy 0.950 or a current checkout and compare the reveal_type result with the expected int. Trace generic property subclass handling and the related issue #11115; done means C().prop is revealed as builtins.int rather than , with a regression test for the case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100