feat(python): extend existing fast range->Series init to lists of ran…

…ges in a Series (#6099)

py-polars/polars/internals/construction.py

@@ -50,7 +50,7 @@
 from polars.dependencies import pandas as pd
 from polars.dependencies import pyarrow as pa
 from polars.exceptions import ShapeError
-from polars.utils import _is_generator, arrlen, threadpool_size
+from polars.utils import _is_generator, arrlen, range_to_series, threadpool_size
 
 if version_info >= (3, 10):
 
@@ -269,6 +269,8 @@ def sequence_to_pyseries(
     if value is not None:
         if is_dataclass(value) or is_namedtuple(value, annotated=True):
             return pli.DataFrame(values).to_struct(name)._s
+        elif isinstance(value, range):
+            values = [range_to_series("", v) for v in values]
         else:
             # for temporal dtypes:
             # * if the values are integer, we take the physical branch.
@@ -319,7 +321,12 @@ def sequence_to_pyseries(
         elif python_dtype in (list, tuple):
             if nested_dtype is None:
                 nested_value = _get_first_non_none(value)
-                nested_dtype = type(nested_value) if nested_value is not None else float
+                if isinstance(nested_value, range):
+                    nested_dtype = list
+                else:
+                    nested_dtype = (
+                        type(nested_value) if nested_value is not None else float
+                    )
 
             # recursively call Series constructor
             if nested_dtype == list:
@@ -391,7 +398,6 @@ def sequence_to_pyseries(
             return PySeries.new_series_list(name, values, strict)
         else:
             constructor = py_type_to_constructor(python_dtype)
-
             if constructor == PySeries.new_object:
                 try:
                     return PySeries.new_from_anyvalues(name, values)

py-polars/polars/internals/series/series.py

@@ -78,6 +78,7 @@
     _time_to_pl_time,
     is_bool_sequence,
     is_int_sequence,
+    range_to_series,
     range_to_slice,
     scale_bytes,
     sphinx_accessor,
@@ -215,17 +216,17 @@ def __init__(
             raise ValueError(
                 f"Given dtype: '{dtype}' is not a valid Polars data type and cannot be converted into one."  # noqa: E501
             )
+
         # Handle case where values are passed as the first argument
-        if name is not None and not isinstance(name, str):
+        if name is None:
+            name = ""
+        elif not isinstance(name, str):
             if values is None:
                 values = name
-                name = None
+                name = ""
             else:
                 raise ValueError("Series name must be a string.")
 
-        if name is None:
-            name = ""
-
         if values is None:
             self._s = sequence_to_pyseries(
                 name, [], dtype=dtype, dtype_if_empty=dtype_if_empty
@@ -234,17 +235,8 @@ def __init__(
             self._s = series_to_pyseries(name, values)
 
         elif isinstance(values, range):
-            self._s = (
-                pli.arange(
-                    low=values.start,
-                    high=values.stop,
-                    step=values.step,
-                    eager=True,
-                    dtype=dtype,
-                )
-                .rename(name, in_place=True)
-                ._s
-            )
+            self._s = range_to_series(name, values, dtype=dtype)._s
+
         elif isinstance(values, Sequence):
             self._s = sequence_to_pyseries(
                 name,

py-polars/polars/utils.py

@@ -21,7 +21,14 @@
 )
 
 import polars.internals as pli
-from polars.datatypes import DataType, Date, Datetime, PolarsDataType, is_polars_dtype
+from polars.datatypes import (
+    DataType,
+    Date,
+    Datetime,
+    Int64,
+    PolarsDataType,
+    is_polars_dtype,
+)
 from polars.dependencies import _ZONEINFO_AVAILABLE, zoneinfo
 
 try:
@@ -170,6 +177,19 @@ def is_str_sequence(
     return isinstance(val, Sequence) and _is_iterable_of(val, str)
 
 
+def range_to_series(
+    name: str, rng: range, dtype: PolarsDataType | None = Int64
+) -> pli.Series:
+    """Fast conversion of the given range to a Series."""
+    return pli.arange(
+        low=rng.start,
+        high=rng.stop,
+        step=rng.step,
+        eager=True,
+        dtype=dtype,
+    ).rename(name, in_place=True)
+
+
 def range_to_slice(rng: range) -> slice:
     """Return the given range as an equivalent slice."""
     return slice(rng.start, rng.stop, rng.step)

py-polars/tests/unit/test_series.py

@@ -1317,9 +1317,25 @@ def test_sqrt() -> None:
 
 
 def test_range() -> None:
-    s = pl.Series("a", [1, 2, 3, 2, 2, 3, 0])
-    assert s[2:5].series_equal(s[range(2, 5)])
-    df = pl.DataFrame([s])
+    s1 = pl.Series("a", [1, 2, 3, 2, 2, 3, 0])
+    assert s1[2:5].series_equal(s1[range(2, 5)])
+
+    ranges = [range(-2, 1), range(3), range(2, 8, 2)]
+
+    s2 = pl.Series("b", ranges, dtype=pl.List(pl.Int8))
+    assert s2.to_list() == [[-2, -1, 0], [0, 1, 2], [2, 4, 6]]
+    assert s2.dtype == pl.List(pl.Int8)
+    assert s2.name == "b"
+
+    s3 = pl.Series("c", (ranges for _ in range(3)))
+    assert s3.to_list() == [
+        [[-2, -1, 0], [0, 1, 2], [2, 4, 6]],
+        [[-2, -1, 0], [0, 1, 2], [2, 4, 6]],
+        [[-2, -1, 0], [0, 1, 2], [2, 4, 6]],
+    ]
+    assert s3.dtype == pl.List(pl.List(pl.Int64))
+
+    df = pl.DataFrame([s1])
     assert df[2:5].frame_equal(df[range(2, 5)])