chore: validate predicates in nw.when one level higher

narwhals-dev · Jan 7, 2025 · f57f894 · f57f894
1 parent a6d76e1
commit f57f894
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Showing 4 changed files with 6 additions and 18 deletions.
diff --git a/narwhals/_arrow/namespace.py b/narwhals/_arrow/namespace.py
@@ -359,12 +359,7 @@ def when(
         *predicates: IntoArrowExpr,
     ) -> ArrowWhen:
         plx = self.__class__(backend_version=self._backend_version, version=self._version)
-        if predicates:
-            condition = plx.all_horizontal(*predicates)
-        else:
-            msg = "at least one predicate needs to be provided"
-            raise TypeError(msg)
-
+        condition = plx.all_horizontal(*predicates)
         return ArrowWhen(condition, self._backend_version, version=self._version)
 
     def concat_str(

diff --git a/narwhals/_dask/namespace.py b/narwhals/_dask/namespace.py
@@ -310,12 +310,7 @@ def when(
         *predicates: IntoDaskExpr,
     ) -> DaskWhen:
         plx = self.__class__(backend_version=self._backend_version, version=self._version)
-        if predicates:
-            condition = plx.all_horizontal(*predicates)
-        else:
-            msg = "at least one predicate needs to be provided"
-            raise TypeError(msg)
-
+        condition = plx.all_horizontal(*predicates)
         return DaskWhen(
             condition, self._backend_version, returns_scalar=False, version=self._version
         )

diff --git a/narwhals/_pandas_like/namespace.py b/narwhals/_pandas_like/namespace.py
@@ -371,12 +371,7 @@ def when(
         plx = self.__class__(
             self._implementation, self._backend_version, version=self._version
         )
-        if predicates:
-            condition = plx.all_horizontal(*predicates)
-        else:
-            msg = "at least one predicate needs to be provided"
-            raise TypeError(msg)
-
+        condition = plx.all_horizontal(*predicates)
         return PandasWhen(
             condition, self._implementation, self._backend_version, version=self._version
         )

diff --git a/narwhals/expr.py b/narwhals/expr.py
@@ -7643,6 +7643,9 @@ def max_horizontal(*exprs: IntoExpr | Iterable[IntoExpr]) -> Expr:
 class When:
     def __init__(self, *predicates: IntoExpr | Iterable[IntoExpr]) -> None:
         self._predicates = flatten([predicates])
+        if not self._predicates:
+            msg = "At least one predicate needs to be provided to `narwhals.when`."
+            raise TypeError(msg)
 
     def _extract_predicates(self, plx: Any) -> Any:
         return [extract_compliant(plx, v) for v in self._predicates]