fix functools.cache and operator.attrgetter

Author: KotlinIsland

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+## [2.9.1]
+### Fixed
+- definition of `functools.cache` and `operator.attrgetter`
+
 ## [2.9.0]
 ### Added
 - `collections.User*` should have `__repr__`

docs/source/based_features.rst

@@ -325,6 +325,26 @@ The defined type of a variable will be shown in the message for `reveal_type`:
     reveal_type(a)  # Revealed type is "int" (narrowed from "object")
 
 
+Typed ``functools.Cache``
+-------------------------
+
+In mypy, ``functools.cache`` is unsafe:
+
+.. code-block:: python
+
+    @cache
+    def f(): ...
+    f(1, 2, 3)  # no error
+
+This is resolved:
+
+.. code-block:: python
+
+    @cache
+    def f(): ...
+    f(1, 2, 3)  # error: expected no args
+
+
 Checked f-strings
 -----------------
 

mypy/test/typetest/__init__.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+from functools import lru_cache
+
+# use `basedtyping` when we drop python 3.8
+from types import MethodType
+from typing import TYPE_CHECKING, Callable
+from typing_extensions import assert_type
+
+from mypy_extensions import Arg
+
+# use `functools.cache` when we drop python 3.8
+cache = lru_cache(None)
+
+
+class A:
+    @cache
+    def m(self, a: list[int]): ...
+
+    @classmethod
+    @cache
+    def c(cls, a: list[int]): ...
+
+    @staticmethod
+    @cache
+    def s(a: list[int]): ...
+
+
+@cache
+def f(a: list[int]): ...
+
+
+if TYPE_CHECKING:
+    from functools import _HashCallable, _LruCacheWrapperBase, _LruCacheWrapperMethod
+
+    ExpectedFunction = _LruCacheWrapperBase[Callable[[Arg(list[int], "a")], None]]
+    ExpectedMethod = _LruCacheWrapperMethod[Callable[[Arg(list[int], "a")], None]]
+    ExpectedMethodNone = _LruCacheWrapperMethod["() -> None"]
+    a = A()
+    a.m([1])  # type: ignore[arg-type]
+    assert_type(a.m, ExpectedMethod)
+    assert_type(a.c, ExpectedMethod)
+    # this is wrong, it shouldn't eat the `a` argument, but this is because of mypy `staticmethod` special casing
+    assert_type(a.s, ExpectedMethodNone)
+    assert_type(a.s, MethodType & (_LruCacheWrapperBase[Callable[[Arg(list[int], "a")], None]] | _HashCallable))  # type: ignore[assert-type]
+    assert_type(f.__get__(1), ExpectedMethodNone)
+    f([1])  # type: ignore[arg-type]

mypy/test/typetest/functools.py

@@ -0,0 +1,6 @@
+from operator import attrgetter
+from typing_extensions import assert_type
+
+
+def check_attrgetter():
+    assert_type(attrgetter("name"), attrgetter[object])

mypy/test/typetest/operator.py

@@ -140,6 +140,7 @@ class staticmethod(Generic[_P, _R_co]):
     @property
     def __isabstractmethod__(self) -> bool: ...
     def __init__(self, f: Callable[_P, _R_co], /) -> None: ...
+    # TODO: doesn't actually return `_NamedCallable`, it returns the callable that was passed to the constructor
     @overload
     def __get__(self, instance: None, owner: type, /) -> _NamedCallable[_P, _R_co]: ...
     @overload

mypy/test/typetest_functools.py

@@ -58,10 +58,9 @@ class _HashCallable(Protocol):
     def __call__(self, /, *args: Hashable, **kwargs: Hashable) -> Never: ...
 
 @type_check_only
-class _LruCacheWrapperBase(Protocol[_out_TCallable]):
-    __wrapped__: Final[_out_TCallable] = ... # type: ignore[misc]
-    __call__: Final[_out_TCallable | _HashCallable] = ... # type: ignore[misc]
-
+class _LruCacheWrapperBase(Generic[_out_TCallable]):
+    __wrapped__: Final[_out_TCallable]  # type: ignore[misc]
+    __call__: Final[_out_TCallable | _HashCallable]  # type: ignore[misc]
 
     def cache_info(self) -> _CacheInfo: ...
     def cache_clear(self) -> None: ...
@@ -71,23 +70,28 @@ class _LruCacheWrapperBase(Protocol[_out_TCallable]):
     def __copy__(self) -> Self: ...
     def __deepcopy__(self, memo: Any, /) -> Self: ...
 
-@final
+
+# replace with `Method & X` once #856 is resolved
+@type_check_only
+class _LruCacheWrapperMethod(MethodType, _LruCacheWrapperBase[_out_TCallable]):  # type: ignore[misc]
+    __call__: Final[_out_TCallable | _HashCallable]  # type: ignore[misc, assignment]
+
+
 # actually defined in `_functools`
+@final
 class _lru_cache_wrapper(_LruCacheWrapperBase[_out_TCallable]):
     def __init__(self, user_function: Never, maxsize: Never, typed: Never, cache_info_type: Never): ...
 
-    # TODO: reintroduce this once mypy 1.14 fork is merged
-    # @overload
-    # def __get__(self, instance: None, owner: object) -> Self: ...
-    # @overload
+    @overload
+    def __get__(self, instance: None, owner: object) -> Self: ...
+    @overload
     def __get__(
         self: _lru_cache_wrapper[Callable[Concatenate[Never, _PWrapped], _RWrapped]],
         instance: object,
         owner: type[object] | None = None,
         /,
-        # ideally, we would capture the Callable here, and intersect with `MethodType`
-    ) ->  _LruCacheWrapperBase[Callable[_PWrapped, _RWrapped]]: ...
-
+    # ideally we could capture the `Callable` to account for subtypes and intersect with `MethodType`
+    ) -> _LruCacheWrapperMethod[Callable[_PWrapped, _RWrapped]]: ...
 
 @overload
 def lru_cache(maxsize: int | None = 128, typed: bool = False) -> FunctionType[[_TCallable], _lru_cache_wrapper[_TCallable]]: ...

mypy/typeshed/stdlib/builtins.pyi

@@ -183,15 +183,15 @@ if sys.version_info >= (3, 11):
 @final
 class attrgetter(Generic[_T_co]):
     @overload
-    def __new__(cls, attr: str, /) -> attrgetter[Any]: ...
+    def __new__(cls, attr: str, /) -> attrgetter[object]: ...
     @overload
-    def __new__(cls, attr: str, attr2: str, /) -> attrgetter[tuple[Any, Any]]: ...
+    def __new__(cls, attr: str, attr2: str, /) -> attrgetter[tuple[object, object]]: ...
     @overload
-    def __new__(cls, attr: str, attr2: str, attr3: str, /) -> attrgetter[tuple[Any, Any, Any]]: ...
+    def __new__(cls, attr: str, attr2: str, attr3: str, /) -> attrgetter[tuple[object, object, object]]: ...
     @overload
-    def __new__(cls, attr: str, attr2: str, attr3: str, attr4: str, /) -> attrgetter[tuple[Any, Any, Any, Any]]: ...
+    def __new__(cls, attr: str, attr2: str, attr3: str, attr4: str, /) -> attrgetter[tuple[object, object, object, object]]: ...
     @overload
-    def __new__(cls, attr: str, /, *attrs: str) -> attrgetter[tuple[Any, ...]]: ...
+    def __new__(cls, attr: str, /, *attrs: str) -> attrgetter[tuple[object, ...]]: ...
     def __call__(self, obj: Any, /) -> _T_co: ...
 
 @final

mypy/typeshed/stdlib/functools.pyi

@@ -73,6 +73,7 @@ _P = ParamSpec("_P")
 
 # Make sure this class definition stays roughly in line with `builtins.function`
 # This class is special-cased
+# is actually `builtins.function`
 @final
 class FunctionType:
     @property
@@ -430,6 +431,7 @@ class CoroutineType(Coroutine[_YieldT_co, _SendT_contra, _ReturnT_co]):
     if sys.version_info >= (3, 13):
         def __class_getitem__(cls, item: Any, /) -> Any: ...
 
+# is actually `builtins.method`
 @final
 class MethodType:
     @property