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enh: Add support for slice(None) in series getitem #3342

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Merged
MarcoGorelli merged 3 commits into from
Dec 12, 2025
+12 −2
Merged

enh: Add support for slice(None) in series getitem #3342

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5945581
enh: Add support for `slice(None)` in series getitem
hoxbro Dec 2, 2025
fff0462
fix typing
hoxbro Dec 2, 2025
593ba1d
Merge branch 'main' into enh_series_slice_none
MarcoGorelli Dec 12, 2025
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9 changes: 8 additions & 1 deletion narwhals/_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1314,7 +1314,11 @@ def is_slice_index(obj: Any) -> TypeIs[_SliceIndex]:
return isinstance(obj, slice) and (
isinstance(obj.start, int)
or isinstance(obj.stop, int)
or (isinstance(obj.step, int) and obj.start is None and obj.stop is None)
or (
isinstance(obj.step, (int, NoneType))
and obj.start is None
and obj.stop is None
)
)


Expand Down Expand Up @@ -2141,3 +2145,6 @@ def __repr__(self) -> str: # pragma: no cover
# the "no_default" sentinel should typically be used when one of the valid parameter
# values is None, as otherwise we cannot determine if the caller has set that value.
no_default = _NoDefault.no_default

# Can be imported from types in Python 3.10
NoneType = type(None)
5 changes: 4 additions & 1 deletion tests/series_only/getitem_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
import pytest

import narwhals as nw
from tests.utils import assert_equal_data
from tests.utils import assert_equal_data, assert_equal_series

if TYPE_CHECKING:
from tests.utils import ConstructorEager
Expand Down Expand Up @@ -38,6 +38,9 @@ def test_by_slice(constructor_eager: ConstructorEager) -> None:
result = {"b": df[[], 1]}
expected = {"b": []}
assert_equal_data(result, expected)
result_ser = df[:, 0][slice(None)]
expected_ser = [1, 2, 3]
assert_equal_series(result_ser, expected_ser, name="a")


def test_getitem_arrow_scalar() -> None:
Expand Down
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