more generic

narwhals/_arrow/dataframe.py

@@ -175,19 +175,22 @@ def with_columns(
         to_concat = []
         output_names = []
         # Make sure to preserve column order
+        length = len(self)
         for name in self.columns:
             if name in new_column_name_to_new_column_map:
                 to_concat.append(
                     validate_dataframe_comparand(
-                        new_column_name_to_new_column_map.pop(name)
+                        length=length, other=new_column_name_to_new_column_map.pop(name)
                     )
                 )
             else:
                 to_concat.append(self._native_dataframe[name])
             output_names.append(name)
         for s in new_column_name_to_new_column_map:
             to_concat.append(
-                validate_dataframe_comparand(new_column_name_to_new_column_map[s])
+                validate_dataframe_comparand(
+                    length=length, other=new_column_name_to_new_column_map[s]
+                )
             )
             output_names.append(s)
         df = self._native_dataframe.__class__.from_arrays(to_concat, names=output_names)

narwhals/_arrow/namespace.py

@@ -126,9 +126,9 @@ def all(self) -> ArrowExpr:
         )
 
     def lit(self, value: Any, dtype: dtypes.DType | None) -> ArrowExpr:
-        def _lit_arrow_series(df: ArrowDataFrame) -> ArrowSeries:
+        def _lit_arrow_series(_: ArrowDataFrame) -> ArrowSeries:
             arrow_series = ArrowSeries._from_iterable(
-                data=[value] * len(df),
+                data=[value],
                 name="lit",
                 backend_version=self._backend_version,
             )

narwhals/_arrow/utils.py

@@ -123,7 +123,7 @@ def validate_column_comparand(other: Any) -> Any:
     return other
 
 
-def validate_dataframe_comparand(other: Any) -> Any:
+def validate_dataframe_comparand(length: int, other: Any) -> Any:
     """Validate RHS of binary operation.
 
     If the comparison isn't supported, return `NotImplemented` so that the
@@ -136,9 +136,8 @@ def validate_dataframe_comparand(other: Any) -> Any:
         return NotImplemented
     if isinstance(other, ArrowSeries):
         if len(other) == 1:
-            # broadcast
-            msg = "not implemented yet"  # pragma: no cover
-            raise NotImplementedError(msg)
+            pa = get_pyarrow()
+            return pa.chunked_array([[other.item()] * length])
         return other._native_series
     msg = "Please report a bug"  # pragma: no cover
     raise AssertionError(msg)