Mypy is expecting `type[Never]` in context when it shouldn't
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Description
Bug Report
I have written (well, copied, from here) a class classproperty to handle implementing class properties. It works perfectly fine, however when I try and type it as follows (which I think is valid), mypy raises the below error
class classproperty[T, C]:
def __init__(self, func: Callable[[type[C]], T]):
self.func = func
def __get__(self, _obj: C, owner: type[C]) -> T:
return self.func(owner)
class Test:
@classproperty
def my_property(cls):
return 1
error: Argument 1 to "classproperty" has incompatible type "Callable[[Test], Any]"; expected "Callable[[type[Never]], Any]" [arg-type]
I don't think this is correct, based on my understanding of descriptors and __get__. I asked a question on stackoverflow about this and it was suggested that this is caused by incorrect assumptions about how __get__ is called
To Reproduce
Gist link here
Expected Behavior
Mypy should pass
Actual Behavior
error: Argument 1 to "classproperty" has incompatible type "Callable[[Test], Any]"; expected "Callable[[type[Never]], Any]" [arg-type]
Your Environment
- Python 3.13.1
mypy==1.15.0
No further config
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 linked mypy-play gist and reduce the classproperty example to a focused reproducer under Python 3.13.1 and mypy 1.15. Read the descriptor and generic inference handling involved in the reported type[Never] expectation. Done means mypy accepts the example and a regression test covers the expected behavior.
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