fix(selectors): resolve typing and coverage CI failures on __xor__

Author: SAY-5

narwhals/_compliant/selectors.py

@@ -310,7 +310,7 @@ def names(df: FrameT) -> Sequence[str]:
             return self.selectors._selector.from_callables(series, names, context=self)
         return self._to_expr() & other
 
-    @overload  # type: ignore[override]
+    @overload
     def __xor__(self, other: Self) -> Self: ...
     @overload
     def __xor__(
@@ -344,10 +344,10 @@ def names(df: FrameT) -> Sequence[str]:
                 ]
 
             return self.selectors._selector.from_callables(series, names, context=self)
-        msg = (
-            f"unsupported operand type(s) for op: ('Selector' ^ '{type(other).__name__}')"
-        )
-        raise TypeError(msg)
+        # The narwhals-level Selector.__xor__ rejects non-selectors before reaching
+        # here, so this branch is a defensive guard only.
+        msg = f"unsupported operand type(s) for op: ('Selector' ^ '{type(other).__name__}')"  # pragma: no cover
+        raise TypeError(msg)  # pragma: no cover
 
     def __invert__(self) -> CompliantSelector[FrameT, SeriesOrExprT]:
         return self.selectors.all() - self

narwhals/_polars/expr.py

@@ -273,13 +273,15 @@ def __or__(self, other: PolarsExpr) -> Self:
         return self._with_native(self.native.__or__(extract_native(other)))
 
     def __xor__(self, other: PolarsExpr) -> Self:
-        if self._backend_version >= (1,):
-            return self._with_native(self.native.__xor__(extract_native(other)))
-        # Polars added Selector.__xor__ in 1.0.0; emulate via existing set ops.
         other_native = extract_native(other)
-        return self._with_native(
-            self.native.__or__(other_native).__sub__(self.native.__and__(other_native))
-        )
+        if self._backend_version < (1,):  # pragma: no cover
+            # Polars added Selector.__xor__ in 1.0.0; emulate via existing set ops.
+            return self._with_native(
+                self.native.__or__(other_native).__sub__(
+                    self.native.__and__(other_native)
+                )
+            )
+        return self._with_native(self.native.__xor__(other_native))
 
     def __add__(self, other: Any) -> Self:
         return self._with_native(self.native.__add__(extract_native(other)))

narwhals/selectors.py

@@ -56,7 +56,7 @@ def __and__(self, other: Any) -> Expr:  # type: ignore[override]
             ExprNode(ExprKind.ELEMENTWISE, "__and__", exprs=(other,), str_as_lit=True)
         )
 
-    def __xor__(self, other: Any) -> Expr:  # type: ignore[override]
+    def __xor__(self, other: Any) -> Expr:
         if isinstance(other, Selector):
             return self._append_node(
                 ExprNode(