@classmethod complaining about the first cls non-optional argument

[sam-goodwin]

Describe the bug
I can't seem to define a class method that accepts the cls parameter. PyRight flags it as a type error.

Code or Screenshots
If possible, provide a minimal, self-contained code sample (surrounded by triple back ticks) to demonstrate the issue. The code should define or import all referenced symbols.

class Foo:
    @classmethod
    def foo(cls):
        ...

I get this error:

Argument of type "(cls: type[Self@Foo]) -> None" cannot be assigned to parameter "f" of type "() -> _R_co@classmethod" in function "__init__"
  Type "(cls: type[Self@Foo]) -> None" cannot be assigned to type "() -> _R_co@classmethod"Pylance[reportArgumentType](https://github.com/microsoft/pyright/blob/main/docs/configuration.md#reportArgumentType)

VS Code extension or command-line
Both CLI and VS Code have the same problem.

• pyright 1.1.358
• ms-python.vscode-pylance v2024.4.1
• Python 3.10.13

[sam-goodwin]

Error goes away if i accept no arguments (as suggested in the type error)

[sam-goodwin]

Definitions of @classmethod in my environment.

class classmethod(Generic[_T, _P, _R_co]):
    @property
    def __func__(self) -> Callable[Concatenate[type[_T], _P], _R_co]: ...
    @property
    def __isabstractmethod__(self) -> bool: ...
    def __init__(self, f: Callable[Concatenate[type[_T], _P], _R_co], /) -> None: ...
    @overload
    def __get__(self, instance: _T, owner: type[_T] | None = None, /) -> Callable[_P, _R_co]: ...
    @overload
    def __get__(self, instance: None, owner: type[_T], /) -> Callable[_P, _R_co]: ...
    if sys.version_info >= (3, 10):
        __name__: str
        __qualname__: str
        @property
        def __wrapped__(self) -> Callable[Concatenate[type[_T], _P], _R_co]: ...

[erictraut]

I'm not able to repro this issue.

https://pyright-play.net/?pythonVersion=3.10&code=MYGwhgzhAEBiD28BcBYAUNT0ACpIQFsBTAFwAt4ATdLaSogM2gcQApQIBKVDWrAOkHogA

My best guess is that you have a really old, stale version of typing_extensions installed in your environment. Please try to repro with a new, clean virtual environment.

I'm pretty confident this isn't a bug in pyright, so I'm going to close the issue.

[sam-goodwin]

My typing_extensions is latest:

typing-extensions==4.11.0

[sam-goodwin]

There is something wrong with the Concatenate type in my setup.

If i monkey patch the classmethod's __init__.py function:

Replace this:

def __init__(self, f: Callable[Concatenate[type[_T], _P], _R_co], /) -> None: ...

With:

def __init__(self, f: Callable[..., _R_co], /) -> None: ...

Then the error goes away.

It looks like Concatenate is always resolving to [] on my machine and therefore always expects zero arguments.

My typesheds in VS Code come from:

.vscode/extensions/ms-python.vscode-pylance-2024.4.1/dist/typeshed-fallback/stdlib/builtins.pyi

But the same errors also happen in CLI which is installed by

pyright==1.1.358

[sam-goodwin]

PyLance is complaining about Concatenate[type[_T], _P]

Expected type expression but received "_ExtensionsSpecialForm"

[sam-goodwin]

Another monkey patch that makes the error go away is to import Concatenate from typing instead of typing_extensions in builtins.pyi.

Got the idea from: python/typing_extensions#48

[erictraut]

It sounds like something in your current environment is corrupt. Have you tried creating a clean virtual environment as I suggested above?

Do you have a typing-extensions stub library installed? Those would override the stubs that ship with pyright or pylance.

[sam-goodwin]

Perhaps I misunderstood what you meant by clean environment. I cleaned it but re-produced it from my requirements.txt.

See here:
https://gist.github.com/sam-goodwin/6834dd69cb7a18d642f37b11a39d6918

If I dial this back to just pyright and no other dependencies, I do indeed see the error go away. Thanks for the lead, I will clean up my dependencies and try and zero in on the culprit.

[sam-goodwin]

Tracked it down to include = ["py.typed"] in a transitive dependency. I am depending on this packyak package (which I own). Removing the py.typed from the wheel fixes the problem.

https://github.com/sam-goodwin/packyak/blob/fd882ec3252aba6894c4f61d74c12e1f0bbe1a03/pyproject.toml#L7