fix: construct list series from any values subject to dtype

py-polars/polars/utils/_construction.py

@@ -267,6 +267,26 @@ def sequence_from_anyvalue_or_object(name: str, values: Sequence[Any]) -> PySeri
         raise
 
 
+def sequence_from_anyvalue_and_dtype_or_object(
+    name: str, values: Sequence[Any], dtype: PolarsDataType
+) -> PySeries:
+    """
+    Last resort conversion.
+
+    AnyValues are most flexible and if they fail we go for object types
+
+    """
+    try:
+        return PySeries.new_from_anyvalues_and_dtype(name, values, dtype, strict=True)
+    # raised if we cannot convert to Wrap<AnyValue>
+    except RuntimeError:
+        return PySeries.new_object(name, values, _strict=False)
+    except ComputeError as exc:
+        if "mixed dtypes" in str(exc):
+            return PySeries.new_object(name, values, _strict=False)
+        raise
+
+
 def iterable_to_pyseries(
     name: str,
     values: Iterable[Any],
@@ -518,7 +538,7 @@ def sequence_to_pyseries(
             if isinstance(dtype, Object):
                 return PySeries.new_object(name, values, strict)
             if dtype:
-                srs = sequence_from_anyvalue_or_object(name, values)
+                srs = sequence_from_anyvalue_and_dtype_or_object(name, values, dtype)
                 if dtype.is_not(srs.dtype()):
                     srs = srs.cast(dtype, strict=False)
                 return srs

py-polars/src/series/construction.rs

@@ -180,6 +180,19 @@ impl PySeries {
         Ok(s.into())
     }
 
+    #[staticmethod]
+    fn new_from_anyvalues_and_dtype(
+        name: &str,
+        val: Vec<Wrap<AnyValue<'_>>>,
+        dtype: Wrap<DataType>,
+        strict: bool,
+    ) -> PyResult<PySeries> {
+        let avs = slice_extract_wrapped(&val);
+        let s = Series::from_any_values_and_dtype(name, avs, &dtype.0, strict)
+            .map_err(PyPolarsErr::from)?;
+        Ok(s.into())
+    }
+
     #[staticmethod]
     fn new_str(name: &str, val: Wrap<Utf8Chunked>, _strict: bool) -> Self {
         val.0.into_series().with_name(name).into()

py-polars/tests/unit/datatypes/test_list.py

@@ -571,3 +571,23 @@ def test_list_inner_cast_physical_11513() -> None:
 def test_list_is_nested_deprecated(dtype: PolarsDataType, expected: bool) -> None:
     with pytest.deprecated_call():
         assert dtype.is_nested is expected
+
+
+def test_list_series_construction_with_dtype_11849_11878() -> None:
+    s = pl.Series([[1, 2], [3.3, 4.9]], dtype=pl.List(pl.Float64))
+    assert s.to_list() == [[1, 2], [3.3, 4.9]]
+
+    s1 = pl.Series([[1, 2], [3.0, 4.0]], dtype=pl.List(pl.Float64))
+    s2 = pl.Series([[1, 2], [3.0, 4.9]], dtype=pl.List(pl.Float64))
+    assert_series_equal(s1 == s2, pl.Series([True, False]))
+
+    s = pl.Series(
+        "groups",
+        [[{"1": "A", "2": None}], [{"1": "B", "2": "C"}, {"1": "D", "2": "E"}]],
+        dtype=pl.List(pl.Struct([pl.Field("1", pl.Utf8), pl.Field("2", pl.Utf8)])),
+    )
+
+    assert s.to_list() == [
+        [{"1": "A", "2": None}],
+        [{"1": "B", "2": "C"}, {"1": "D", "2": "E"}],
+    ]