try fixup

narwhals/_arrow/series.py

@@ -474,12 +474,9 @@ def tail(self: Self, n: int) -> Self:
             return self._from_native_series(ser.slice(abs(n)))
 
     def is_in(self: Self, other: Any) -> Self:
-        if isinstance(other, list) and isinstance(other[0], self.__class__):
-            # We can't use `broadcast_and_align` because we don't want to align here.
-            # `other` is just a sequence that all rows from `self` are checked against.
-            value_set = other[0]._native_series
-        else:
-            value_set = pa.array(other)
+        value_set = (
+            other if isinstance(other, pa.ChunkedArray) else pa.chunked_array([other])
+        )
         ser = self._native_series
         return self._from_native_series(pc.is_in(ser, value_set=value_set))
 

narwhals/_pandas_like/series.py

@@ -300,10 +300,6 @@ def is_between(
 
     def is_in(self: Self, other: Any) -> PandasLikeSeries:
         ser = self._native_series
-        if isinstance(other, list) and isinstance(other[0], self.__class__):
-            # We can't use `broadcast_and_align` because we don't want to align here.
-            # `other` is just a sequence that all rows from `self` are checked against.
-            other = other[0]._native_series
         res = ser.isin(other)
         return self._from_native_series(res)
 

narwhals/expr.py

@@ -1251,9 +1251,13 @@ def is_in(self: Self, other: Any) -> Self:
             |   3  10  False   |
             └──────────────────┘
         """
+        from narwhals.series import Series
+
         if isinstance(other, Iterable) and not isinstance(other, (str, bytes)):
             return self.__class__(
-                lambda plx: self._to_compliant_expr(plx).is_in(other),
+                lambda plx: self._to_compliant_expr(plx).is_in(
+                    other.to_native() if isinstance(other, Series) else other
+                ),
                 self._metadata,
             )
         else:

narwhals/series.py

@@ -800,7 +800,9 @@ def is_in(self: Self, other: Any) -> Self:
             ]
         """
         return self._from_compliant_series(
-            self._compliant_series.is_in(self._extract_native(other))
+            self._compliant_series.is_in(
+                other.to_native() if isinstance(other, self.__class__) else other
+            )
         )
 
     def arg_true(self: Self) -> Self: