allow arbitrary types in set difference (#15160)

Author: randolf-scholz

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

@@ -0,0 +1,14 @@
+from typing_extensions import Literal, 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.
+#   For instance, set[Literal] - set[str] should be legal.
+def test_set_difference(x: set[Literal["foo", "bar"]], y: set[str], z: set[int]) -> None:
+    assert_type(x - y, set[Literal["foo", "bar"]])
+    assert_type(y - x, set[str])
+    assert_type(x - z, set[Literal["foo", "bar"]])
+    assert_type(z - x, set[int])
+    assert_type(y - z, set[str])
+    assert_type(z - y, set[int])

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: ...