fix: Always accept {Expr,Series}.is_in(other: Iterable)

narwhals/_arrow/series.py

@@ -585,7 +585,7 @@ def tail(self, n: int) -> Self:
             return self._with_native(self.native.slice(max(0, num_rows - n)))
         return self._with_native(self.native.slice(abs(n)))
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Sequence[Any] | ChunkedArrayAny) -> Self:
         if self._is_native(other):
             value_set: ArrayOrChunkedArray = other
         else:

narwhals/_compliant/column.py

@@ -170,7 +170,7 @@ def is_duplicated(self) -> Self:
 
     def is_finite(self) -> Self: ...
     def is_first_distinct(self) -> Self: ...
-    def is_in(self, other: Any) -> Self: ...
+    def is_in(self, other: Sequence[Any]) -> Self: ...
     def is_last_distinct(self) -> Self: ...
     def is_nan(self) -> Self: ...
     def is_null(self) -> Self: ...

narwhals/_compliant/expr.py

@@ -39,7 +39,7 @@
 if TYPE_CHECKING:
     from collections.abc import Mapping, Sequence
 
-    from typing_extensions import Self, TypeIs
+    from typing_extensions import Self, TypeAlias, TypeIs
 
     from narwhals._compliant.namespace import CompliantNamespace, EagerNamespace
     from narwhals._compliant.series import CompliantSeries
@@ -61,6 +61,8 @@
 
 __all__ = ["CompliantExpr", "DepthTrackingExpr", "EagerExpr", "LazyExpr", "NativeExpr"]
 
+Incomplete: TypeAlias = "Any"
+
 
 class NativeExpr(Protocol):
     """An `Expr`-like object from a package with [Lazy-only support](https://narwhals-dev.github.io/narwhals/extending/#levels-of-support).
@@ -613,7 +615,7 @@ def fill_null(
             "fill_null", value=value, scalar_kwargs={"strategy": strategy, "limit": limit}
         )
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Sequence[Any] | Incomplete) -> Self:
         return self._reuse_series("is_in", other=other)
 
     def arg_true(self) -> Self:

narwhals/_compliant/series.py

@@ -139,6 +139,7 @@ def head(self, n: int) -> Self: ...
     def is_empty(self) -> bool:
         return self.len() == 0
 
+    def is_in(self, other: Sequence[Any] | NativeSeriesT) -> Self: ...
     def is_sorted(self, *, descending: bool) -> bool: ...
     def item(self, index: int | None) -> Any: ...
     def kurtosis(self) -> float | None: ...

narwhals/_dask/expr.py

@@ -611,7 +611,7 @@ def func(expr: dx.Series) -> dx.Series:
 
         return self._with_callable(func, "is_unique")
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Sequence[Any]) -> Self:
         return self._with_callable(lambda expr: expr.isin(other), "is_in")
 
     def null_count(self) -> Self:

narwhals/_pandas_like/series.py

@@ -62,7 +62,7 @@
 
     PandasHistData: TypeAlias = "HistData[pd.Series[Any], list[float]]"
 
-
+Incomplete: TypeAlias = "Any"
 PANDAS_TO_NUMPY_DTYPE_NO_MISSING = {
     "Int64": "int64",
     "int64[pyarrow]": "int64",
@@ -109,7 +109,7 @@
 }
 
 
-class PandasLikeSeries(EagerSeries[Any]):
+class PandasLikeSeries(EagerSeries[Incomplete]):
     def __init__(
         self, native_series: Any, *, implementation: Implementation, version: Version
     ) -> None:
@@ -125,7 +125,7 @@ def __init__(
         self._broadcast = False
 
     @property
-    def native(self) -> Any:
+    def native(self) -> Incomplete:
         return self._native_series
 
     def __native_namespace__(self) -> ModuleType:
@@ -362,7 +362,7 @@ def is_between(
             assert_never(closed)
         return self._with_native(res).alias(ser.name)
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Sequence[Any] | Incomplete) -> Self:
         return self._with_native(self.native.isin(other))
 
     def arg_true(self) -> Self:

narwhals/_utils.py

@@ -47,6 +47,7 @@
     is_numpy_array_1d_int,
     is_pandas_like_dataframe,
     is_pandas_like_series,
+    is_polars_series,
 )
 from narwhals.exceptions import ColumnNotFoundError, DuplicateError, InvalidOperationError
 
@@ -124,6 +125,7 @@
         CompliantLazyFrame,
         CompliantSeries,
         DTypes,
+        EagerAllowed,
         FileSource,
         IntoSeriesT,
         MultiIndexSelector,
@@ -2120,3 +2122,57 @@ def extend_bool(
     Stolen from https://github.com/pola-rs/polars/blob/b8bfb07a4a37a8d449d6d1841e345817431142df/py-polars/polars/_utils/various.py#L580-L594
     """
     return (value,) * n_match if isinstance(value, bool) else tuple(value)
+
+
+class _CanTo_List(Protocol):  # noqa: N801
+    def to_list(self, *args: Any, **kwds: Any) -> list[Any]: ...
+
+
+class _CanToList(Protocol):
+    def tolist(self, *args: Any, **kwds: Any) -> list[Any]: ...
+
+
+class _CanTo_PyList(Protocol):  # noqa: N801
+    def to_pylist(self, *args: Any, **kwds: Any) -> list[Any]: ...
+
+
+def can_to_list(obj: Any) -> TypeIs[_CanTo_List]:
+    return (
+        is_narwhals_series(obj)
+        or is_polars_series(obj)
+        or _hasattr_static(obj, "to_list")
+    )
+
+
+def can_tolist(obj: Any) -> TypeIs[_CanToList]:
+    return is_numpy_array_1d(obj) or _hasattr_static(obj, "tolist")
+
+
+def can_to_pylist(obj: Any) -> TypeIs[_CanTo_PyList]:
+    return (
+        (pa := get_pyarrow()) and isinstance(obj, (pa.Array, pa.ChunkedArray))
+    ) or _hasattr_static(obj, "to_pylist")
+
+
+# TODO @dangotbanned: Add (brief) doc
+def iterable_to_sequence(
+    iterable: Iterable[Any], /, *, backend: EagerAllowed | None = None
+) -> Sequence[Any]:
+    result: Sequence[Any]
+    if backend is not None:
+        from narwhals.series import Series
+
+        result = Series.from_iterable("", iterable, backend=backend).to_list()
+    elif isinstance(iterable, (tuple, list)):
+        result = iterable
+    elif isinstance(iterable, (Iterator, Sequence)):
+        result = tuple(iterable)
+    elif can_to_list(iterable):
+        result = iterable.to_list()
+    elif can_tolist(iterable):
+        result = iterable.tolist()
+    elif can_to_pylist(iterable):
+        result = iterable.to_pylist()
+    else:
+        result = tuple(iterable)
+    return result

narwhals/expr.py

@@ -9,8 +9,14 @@
     ExprMetadata,
     apply_n_ary_operation,
     combine_metadata,
+    is_series,
+)
+from narwhals._utils import (
+    _validate_rolling_arguments,
+    ensure_type,
+    flatten,
+    iterable_to_sequence,
 )
-from narwhals._utils import _validate_rolling_arguments, ensure_type, flatten
 from narwhals.dtypes import _validate_dtype
 from narwhals.exceptions import ComputeError, InvalidOperationError
 from narwhals.expr_cat import ExprCatNamespace
@@ -19,7 +25,6 @@
 from narwhals.expr_name import ExprNameNamespace
 from narwhals.expr_str import ExprStringNamespace
 from narwhals.expr_struct import ExprStructNamespace
-from narwhals.translate import to_native
 
 if TYPE_CHECKING:
     from typing import NoReturn, TypeVar
@@ -968,7 +973,7 @@ def is_between(
             upper_bound,
         )
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Iterable[Any]) -> Self:
         """Check if elements of this expression are present in the other iterable.
 
         Arguments:
@@ -991,10 +996,10 @@ def is_in(self, other: Any) -> Self:
             └──────────────────┘
         """
         if isinstance(other, Iterable) and not isinstance(other, (str, bytes)):
+            other = other.to_native() if is_series(other) else iterable_to_sequence(other)
             return self._with_elementwise(
-                lambda plx: self._to_compliant_expr(plx).is_in(
-                    to_native(other, pass_through=True)
-                )
+                # TODO @dangotbanned: Fix after getting feedback on https://github.com/narwhals-dev/narwhals/pull/3207#discussion_r2430089632
+                lambda plx: self._to_compliant_expr(plx).is_in(other)  # pyright: ignore[reportArgumentType]
             )
         msg = "Narwhals `is_in` doesn't accept expressions as an argument, as opposed to Polars. You should provide an iterable instead."
         raise NotImplementedError(msg)

narwhals/series.py

@@ -14,6 +14,7 @@
     is_compliant_series,
     is_eager_allowed,
     is_index_selector,
+    iterable_to_sequence,
     qualified_type_name,
     supports_arrow_c_stream,
 )
@@ -25,7 +26,6 @@
 from narwhals.series_list import SeriesListNamespace
 from narwhals.series_str import SeriesStringNamespace
 from narwhals.series_struct import SeriesStructNamespace
-from narwhals.translate import to_native
 from narwhals.typing import IntoSeriesT
 
 if TYPE_CHECKING:
@@ -926,7 +926,7 @@ def last(self) -> PythonLiteral:
         """
         return self._compliant_series.last()
 
-    def is_in(self, other: Any) -> Self:
+    def is_in(self, other: Iterable[Any]) -> Self:
         """Check if the elements of this Series are in the other sequence.
 
         Arguments:
@@ -948,9 +948,12 @@ def is_in(self, other: Any) -> Self:
               ]
             ]
         """
-        return self._with_compliant(
-            self._compliant_series.is_in(to_native(other, pass_through=True))
+        other = (
+            other.to_native()
+            if isinstance(other, Series)
+            else iterable_to_sequence(other, backend=self.implementation)
         )
+        return self._with_compliant(self._compliant_series.is_in(other))
 
     def arg_true(self) -> Self:
         """Find elements where boolean Series is True.