feat: Broadcast scalar input for list.slice

crates/polars-expr/src/dispatch/list.rs

@@ -153,6 +153,11 @@ pub(super) fn slice(args: &mut [Column]) -> PolarsResult<Column> {
             return Ok(list_ca.lst_slice(offset, slice_len).into_column());
         },
         (1, length_slice_len) => {
+            let list_ca = if list_ca.len() == 1 {
+                list_ca.new_from_index(0, length_slice_len)
+            } else {
+                list_ca.clone()
+            };
             check_slice_arg_shape(length_slice_len, list_ca.len(), "length")?;
             let offset = offset_s.get(0).unwrap().try_extract::<i64>()?;
             // cast to i64 as it is more likely that it is that dtype

py-polars/tests/unit/operations/namespaces/list/test_list.py

@@ -1366,3 +1366,16 @@ def test_list_sample_fraction_with_replacement_27344() -> None:
 
     result = df.select(pl.col("x").list.sample(fraction=2, with_replacement=True))
     assert result["x"][0].to_list() == [1, 1]
+
+
+def test_list_slice_broadcast_27480() -> None:
+    result = pl.select(
+        pl.lit([0, 1, 2]).list.slice(0, pl.lit(pl.Series([1, 2, 3]))).alias("broadcast")
+    )
+    expected = pl.select(
+        pl.repeat(pl.lit([0, 1, 2]), 3)
+        .list.slice(0, pl.lit(pl.Series([1, 2, 3])))
+        .alias("broadcast")
+    )
+
+    assert_frame_equal(result, expected)