feat: dask sum_horizontal (#775)

* feat: dask sum_horizontal

narwhals/_arrow/namespace.py

@@ -167,25 +167,13 @@ def _lit_arrow_series(_: ArrowDataFrame) -> ArrowSeries:
         )
 
     def all_horizontal(self, *exprs: IntoArrowExpr) -> ArrowExpr:
-        return reduce(
-            lambda x, y: x & y,
-            parse_into_exprs(*exprs, namespace=self),
-        )
+        return reduce(lambda x, y: x & y, parse_into_exprs(*exprs, namespace=self))
 
     def any_horizontal(self, *exprs: IntoArrowExpr) -> ArrowExpr:
-        return reduce(
-            lambda x, y: x | y,
-            parse_into_exprs(*exprs, namespace=self),
-        )
+        return reduce(lambda x, y: x | y, parse_into_exprs(*exprs, namespace=self))
 
     def sum_horizontal(self, *exprs: IntoArrowExpr) -> ArrowExpr:
-        return reduce(
-            lambda x, y: x + y,
-            parse_into_exprs(
-                *exprs,
-                namespace=self,
-            ),
-        )
+        return reduce(lambda x, y: x + y, parse_into_exprs(*exprs, namespace=self))
 
     def concat(
         self,

narwhals/_dask/namespace.py

@@ -133,6 +133,9 @@ def all_horizontal(self, *exprs: IntoDaskExpr) -> DaskExpr:
     def any_horizontal(self, *exprs: IntoDaskExpr) -> DaskExpr:
         return reduce(lambda x, y: x | y, parse_into_exprs(*exprs, namespace=self))
 
+    def sum_horizontal(self, *exprs: IntoDaskExpr) -> DaskExpr:
+        return reduce(lambda x, y: x + y, parse_into_exprs(*exprs, namespace=self))
+
     def _create_expr_from_series(self, _: Any) -> NoReturn:
         msg = "`_create_expr_from_series` for DaskNamespace exists only for compatibility"
         raise NotImplementedError(msg)

narwhals/_pandas_like/namespace.py

@@ -202,25 +202,13 @@ def len(self) -> PandasLikeExpr:
 
     # --- horizontal ---
     def sum_horizontal(self, *exprs: IntoPandasLikeExpr) -> PandasLikeExpr:
-        return reduce(
-            lambda x, y: x + y,
-            parse_into_exprs(
-                *exprs,
-                namespace=self,
-            ),
-        )
+        return reduce(lambda x, y: x + y, parse_into_exprs(*exprs, namespace=self))
 
     def all_horizontal(self, *exprs: IntoPandasLikeExpr) -> PandasLikeExpr:
-        return reduce(
-            lambda x, y: x & y,
-            parse_into_exprs(*exprs, namespace=self),
-        )
+        return reduce(lambda x, y: x & y, parse_into_exprs(*exprs, namespace=self))
 
     def any_horizontal(self, *exprs: IntoPandasLikeExpr) -> PandasLikeExpr:
-        return reduce(
-            lambda x, y: x | y,
-            parse_into_exprs(*exprs, namespace=self),
-        )
+        return reduce(lambda x, y: x | y, parse_into_exprs(*exprs, namespace=self))
 
     def concat(
         self,

tests/expr_and_series/sum_horizontal_test.py

@@ -7,9 +7,7 @@
 
 
 @pytest.mark.parametrize("col_expr", [nw.col("a"), "a"])
-def test_sumh(constructor: Any, col_expr: Any, request: Any) -> None:
-    if "dask" in str(constructor):
-        request.applymarker(pytest.mark.xfail)
+def test_sumh(constructor: Any, col_expr: Any) -> None:
     data = {"a": [1, 3, 2], "b": [4, 4, 6], "z": [7.0, 8, 9]}
     df = nw.from_native(constructor(data))
     result = df.with_columns(horizontal_sum=nw.sum_horizontal(col_expr, nw.col("b")))

tests/test_selectors.py

@@ -7,7 +7,7 @@
 import pytest
 
 import narwhals.stable.v1 as nw
-from narwhals.dependencies import get_dask
+from narwhals.dependencies import get_dask_dataframe
 from narwhals.selectors import all
 from narwhals.selectors import boolean
 from narwhals.selectors import by_dtype
@@ -67,7 +67,7 @@ def test_categorical(request: Any, constructor: Any) -> None:
     compare_dicts(result, expected)
 
 
-@pytest.mark.skipif((get_dask() is None), reason="too old for dask")
+@pytest.mark.skipif((get_dask_dataframe() is None), reason="too old for dask")
 def test_dask_categorical() -> None:
     import dask.dataframe as dd