allow arbitrary types in set difference

Author: randolf-scholz

stdlib/@tests/test_cases/builtins/check_set.py

@@ -0,0 +1,7 @@
+from typing_extensions import assert_type
+
+# Note: type checkers / linters are free to point out that the set difference
+#   below is redundant. But typeshed should allow it, as its job is to describe
+#   what is legal in Python, not what is sensible.
+x: set[str] = {"foo", "bar"}
+assert_type(x - {123}, set[str])

stdlib/builtins.pyi

@@ -1282,7 +1282,7 @@ class set(MutableSet[_T]):
     def __iand__(self, value: AbstractSet[object], /) -> Self: ...
     def __or__(self, value: AbstractSet[_S], /) -> set[_T | _S]: ...
     def __ior__(self, value: AbstractSet[_T], /) -> Self: ...  # type: ignore[override,misc]
-    def __sub__(self, value: AbstractSet[_T | None], /) -> set[_T]: ...
+    def __sub__(self, value: AbstractSet[object], /) -> set[_T]: ...
     def __isub__(self, value: AbstractSet[object], /) -> Self: ...
     def __xor__(self, value: AbstractSet[_S], /) -> set[_T | _S]: ...
     def __ixor__(self, value: AbstractSet[_T], /) -> Self: ...  # type: ignore[override,misc]
@@ -1313,7 +1313,7 @@ class frozenset(AbstractSet[_T_co]):
     def __iter__(self) -> Iterator[_T_co]: ...
     def __and__(self, value: AbstractSet[_T_co], /) -> frozenset[_T_co]: ...
     def __or__(self, value: AbstractSet[_S], /) -> frozenset[_T_co | _S]: ...
-    def __sub__(self, value: AbstractSet[_T_co], /) -> frozenset[_T_co]: ...
+    def __sub__(self, value: AbstractSet[object], /) -> frozenset[_T_co]: ...
     def __xor__(self, value: AbstractSet[_S], /) -> frozenset[_T_co | _S]: ...
     def __le__(self, value: AbstractSet[object], /) -> bool: ...
     def __lt__(self, value: AbstractSet[object], /) -> bool: ...