fix: raise on selectors addition (#1854)

narwhals/_arrow/selectors.py

@@ -2,7 +2,6 @@
 
 from typing import TYPE_CHECKING
 from typing import Any
-from typing import NoReturn
 from typing import Sequence
 
 from narwhals._arrow.expr import ArrowExpr
@@ -178,12 +177,3 @@ def __invert__(self: Self) -> ArrowSelector:
             ).all()
             - self
         )
-
-    def __rsub__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __rand__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __ror__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError

narwhals/_dask/selectors.py

@@ -2,7 +2,6 @@
 
 from typing import TYPE_CHECKING
 from typing import Any
-from typing import NoReturn
 
 from narwhals._dask.expr import DaskExpr
 from narwhals.utils import import_dtypes_module
@@ -186,12 +185,3 @@ def __invert__(self: Self) -> DaskSelector:
             ).all()
             - self
         )
-
-    def __rsub__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __rand__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __ror__(self: Self, other: Any) -> NoReturn:
-        raise NotImplementedError

narwhals/_pandas_like/selectors.py

@@ -2,7 +2,6 @@
 
 from typing import TYPE_CHECKING
 from typing import Any
-from typing import NoReturn
 
 from narwhals._pandas_like.expr import PandasLikeExpr
 from narwhals.utils import import_dtypes_module
@@ -189,12 +188,3 @@ def __invert__(self: Self) -> PandasSelector:
             ).all()
             - self
         )
-
-    def __rsub__(self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __rand__(self, other: Any) -> NoReturn:
-        raise NotImplementedError
-
-    def __ror__(self, other: Any) -> NoReturn:
-        raise NotImplementedError

narwhals/selectors.py

@@ -1,12 +1,39 @@
 from __future__ import annotations
 
+from typing import TYPE_CHECKING
 from typing import Any
+from typing import NoReturn
 
 from narwhals.expr import Expr
 from narwhals.utils import flatten
 
+if TYPE_CHECKING:
+    from typing_extensions import Self
 
-class Selector(Expr): ...
+
+class Selector(Expr):
+    def _to_expr(self: Self) -> Expr:
+        return Expr(
+            to_compliant_expr=self._to_compliant_expr,
+            is_order_dependent=self._is_order_dependent,
+            changes_length=self._changes_length,
+            aggregates=self._aggregates,
+        )
+
+    def __add__(self: Self, other: Any) -> Expr:  # type: ignore[override]
+        if isinstance(other, Selector):
+            msg = "unsupported operand type(s) for op: ('Selector' + 'Selector')"
+            raise TypeError(msg)
+        return self._to_expr() + other  # type: ignore[no-any-return]
+
+    def __rsub__(self: Self, other: Any) -> NoReturn:
+        raise NotImplementedError
+
+    def __rand__(self: Self, other: Any) -> NoReturn:
+        raise NotImplementedError
+
+    def __ror__(self: Self, other: Any) -> NoReturn:
+        raise NotImplementedError
 
 
 def by_dtype(*dtypes: Any) -> Expr:

tests/selectors_test.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
-import pandas as pd
-import pyarrow as pa
+import re
+
 import pytest
 
 import narwhals.stable.v1 as nw
@@ -103,16 +103,17 @@ def test_set_ops(
     assert sorted(result) == expected
 
 
-@pytest.mark.parametrize("invalid_constructor", [pd.DataFrame, pa.table])
-def test_set_ops_invalid(
-    invalid_constructor: Constructor, request: pytest.FixtureRequest
-) -> None:
-    if "duckdb" in str(invalid_constructor):
-        request.applymarker(pytest.mark.xfail)
-    df = nw.from_native(invalid_constructor(data))
+def test_set_ops_invalid(constructor: Constructor) -> None:
+    df = nw.from_native(constructor(data))
     with pytest.raises((NotImplementedError, ValueError)):
         df.select(1 - numeric())
     with pytest.raises((NotImplementedError, ValueError)):
         df.select(1 | numeric())
     with pytest.raises((NotImplementedError, ValueError)):
         df.select(1 & numeric())
+
+    with pytest.raises(
+        TypeError,
+        match=re.escape("unsupported operand type(s) for op: ('Selector' + 'Selector')"),
+    ):
+        df.select(boolean() + numeric())