[skip-ci] wip

narwhals/expr.py

@@ -1254,6 +1254,9 @@ def is_in(self: Self, other: Any) -> Self:
         from narwhals.series import Series
 
         if isinstance(other, Iterable) and not isinstance(other, (str, bytes)):
+            # In the eager case, `other` is allowed to be a Series. However,
+            # we don't allow expressiions. So, to avoid special-casing, we
+            # just call `to_native` here if `other` is a Series.
             return self.__class__(
                 lambda plx: self._to_compliant_expr(plx).is_in(
                     other.to_native() if isinstance(other, Series) else other

narwhals/series.py

@@ -799,6 +799,9 @@ def is_in(self: Self, other: Any) -> Self:
               ]
             ]
         """
+        # In the eager case, `other` is allowed to be a Series. However,
+        # we don't allow expressiions. So, to avoid special-casing, we
+        # just call `to_native` here if `other` is a Series.
         return self._from_compliant_series(
             self._compliant_series.is_in(
                 other.to_native() if isinstance(other, self.__class__) else other

tests/expr_and_series/is_between_test.py

@@ -3,6 +3,7 @@
 from typing import Literal
 
 import pytest
+from datetime import datetime
 
 import narwhals.stable.v1 as nw
 from tests.utils import Constructor
@@ -30,6 +31,27 @@ def test_is_between(
     expected_dict = {"a": expected}
     assert_equal_data(result, expected_dict)
 
+@pytest.mark.parametrize(
+    ("closed", "expected"),
+    [
+        ("left", [False, False]),
+        ("right", [False, True]),
+        ("both", [False, True]),
+        ("none", [False, False]),
+    ],
+)
+def test_is_between_datetimes(
+    constructor: Constructor,
+    closed: Literal["left", "right", "none", "both"],
+    expected: list[bool],
+) -> None:
+    data = {"a": [datetime(2020,1,1), datetime(2020,6,1)]}
+    df = nw.from_native(constructor(data))
+    result = df.select(nw.col("a").is_between(datetime(2020,3,1), datetime(2020,6,1), closed=closed))
+    expected_dict = {"a": expected}
+    assert_equal_data(result, expected_dict)
+
+
 
 def test_is_between_expressified(constructor: Constructor) -> None:
     data = {"a": [1, 4, 2, 5], "b": [0, 5, 2, 4], "c": [9, 9, 9, 9]}