fix pylint E1120 error. (#21230)

* fix pylint E1120 error.

* fix type annotation for py39

* fix mypy error.

* fix mypy error.

* fix mypy error.

* fix wrapper return type.

* refactored `_restricted_classmethod_impl`

* revert refactor

* ignore mypy error.

* resume original type.

* revert mypy.

* attempt fixing macos doctest

---------

Co-authored-by: Jirka Borovec <[email protected]>
Co-authored-by: Nicki Skafte Detlefsen <[email protected]>
Co-authored-by: Justus Schock <[email protected]>

Author: 4 people

src/lightning/pytorch/utilities/model_helpers.py

@@ -19,7 +19,7 @@
 
 from lightning_utilities.core.imports import RequirementCache
 from torch import nn
-from typing_extensions import Concatenate, ParamSpec
+from typing_extensions import Concatenate, ParamSpec, override
 
 import lightning.pytorch as pl
 
@@ -104,26 +104,32 @@ def _check_mixed_imports(instance: object) -> None:
 _R_co = TypeVar("_R_co", covariant=True)  # return type of the decorated method
 
 
-class _restricted_classmethod_impl(Generic[_T, _R_co, _P]):
+class _restricted_classmethod_impl(classmethod, Generic[_T, _P, _R_co]):
     """Drop-in replacement for @classmethod, but raises an exception when the decorated method is called on an instance
     instead of a class type."""
 
+    method: Callable[Concatenate[type[_T], _P], _R_co]
+
     def __init__(self, method: Callable[Concatenate[type[_T], _P], _R_co]) -> None:
+        super().__init__(method)
         self.method = method
 
-    def __get__(self, instance: Optional[_T], cls: type[_T]) -> Callable[_P, _R_co]:
+    @override
+    def __get__(self, instance: _T, cls: Optional[type[_T]] = None) -> Callable[_P, _R_co]:  # type: ignore[override]
         # The wrapper ensures that the method can be inspected, but not called on an instance
         @functools.wraps(self.method)
         def wrapper(*args: Any, **kwargs: Any) -> _R_co:
             # Workaround for https://github.com/pytorch/pytorch/issues/67146
             is_scripting = any(os.path.join("torch", "jit") in frameinfo.filename for frameinfo in inspect.stack())
+            cls_type = cls if cls is not None else type(instance)
             if instance is not None and not is_scripting:
                 raise TypeError(
-                    f"The classmethod `{cls.__name__}.{self.method.__name__}` cannot be called on an instance."
+                    f"The classmethod `{cls_type.__name__}.{self.method.__name__}` cannot be called on an instance."
                     " Please call it on the class type and make sure the return value is used."
                 )
-            return self.method(cls, *args, **kwargs)
+            return self.method(cls_type, *args, **kwargs)
 
+        wrapper.__func__ = self.method
         return wrapper