builtins: Fix typing of reversed (#10655)

Author: plokmijnuhby

stdlib/builtins.pyi

@@ -1634,9 +1634,9 @@ def quit(code: sys._ExitCode = None) -> NoReturn: ...
 
 class reversed(Iterator[_T]):
     @overload
-    def __init__(self, __sequence: Reversible[_T]) -> None: ...
+    def __new__(cls, __sequence: Reversible[_T]) -> Iterator[_T]: ...  # type: ignore[misc]
     @overload
-    def __init__(self, __sequence: SupportsLenAndGetItem[_T]) -> None: ...
+    def __new__(cls, __sequence: SupportsLenAndGetItem[_T]) -> Iterator[_T]: ...  # type: ignore[misc]
     def __iter__(self) -> Self: ...
     def __next__(self) -> _T: ...
     def __length_hint__(self) -> int: ...

test_cases/stdlib/builtins/check_reversed.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+from typing import Generic, TypeVar
+from typing_extensions import assert_type
+
+x: list[int] = []
+assert_type(list(reversed(x)), "list[int]")
+
+
+class MyReversible:
+    def __iter__(self) -> Iterator[str]:
+        yield "blah"
+
+    def __reversed__(self) -> Iterator[str]:
+        yield "blah"
+
+
+assert_type(list(reversed(MyReversible())), "list[str]")
+
+
+_T = TypeVar("_T")
+
+
+class MyLenAndGetItem(Generic[_T]):
+    def __len__(self) -> int:
+        return 0
+
+    def __getitem__(self, item: int) -> _T:
+        raise KeyError
+
+
+len_and_get_item: MyLenAndGetItem[int] = MyLenAndGetItem()
+assert_type(list(reversed(len_and_get_item)), "list[int]")