From 598ca603a6844a12768fa72a8e456a5c3476f0cf Mon Sep 17 00:00:00 2001
From: Marshall Crumiller <mcrumiller@gmail.com>
Date: Thu, 2 May 2024 10:11:43 -0400
Subject: [PATCH] Convert date/datetime in lit construction

---
 py-polars/polars/functions/lit.py             | 16 ++++++-
 .../tests/unit/namespaces/test_datetime.py    | 46 +++++++++++++++++++
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/py-polars/polars/functions/lit.py b/py-polars/polars/functions/lit.py
index b636d5f2544a6..b60c8cb9b9754 100644
--- a/py-polars/polars/functions/lit.py
+++ b/py-polars/polars/functions/lit.py
@@ -77,6 +77,9 @@ def lit(
     time_unit: TimeUnit
 
     if isinstance(value, datetime):
+        if dtype == Date:
+            dt_int = date_to_int(value.date())
+            return lit(dt_int).cast(Date)
         if dtype is not None and (tu := getattr(dtype, "time_unit", "us")) is not None:
             time_unit = tu  # type: ignore[assignment]
         else:
@@ -113,8 +116,17 @@ def lit(
         return lit(time_int).cast(Time)
 
     elif isinstance(value, date):
-        date_int = date_to_int(value)
-        return lit(date_int).cast(Date)
+        if dtype == Datetime:
+            time_unit = getattr(dtype, "time_unit", "us") or "us"
+            dt_utc = datetime(value.year, value.month, value.day)
+            dt_int = datetime_to_int(dt_utc, time_unit)
+            expr = lit(dt_int).cast(Datetime(time_unit))
+            if (time_zone := getattr(dtype, "time_zone", None)) is not None:
+                expr = expr.dt.replace_time_zone(str(time_zone))
+            return expr
+        else:
+            date_int = date_to_int(value)
+            return lit(date_int).cast(Date)
 
     elif isinstance(value, pl.Series):
         value = value._s
diff --git a/py-polars/tests/unit/namespaces/test_datetime.py b/py-polars/tests/unit/namespaces/test_datetime.py
index 5307a2e7e129e..2e3e0f4d53b2e 100644
--- a/py-polars/tests/unit/namespaces/test_datetime.py
+++ b/py-polars/tests/unit/namespaces/test_datetime.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from collections import OrderedDict
 from datetime import date, datetime, time, timedelta
 from typing import TYPE_CHECKING
 
@@ -1310,3 +1311,48 @@ def test_agg_median_expr() -> None:
     )
 
     assert_frame_equal(df.select(pl.all().median()), expected)
+
+
+@pytest.mark.parametrize(
+    ("value_in", "dtype", "expected_value"),
+    [
+        (date(2024, 1, 1), pl.Date, date(2024, 1, 1)),
+        (date(2024, 1, 1), pl.Datetime, datetime(2024, 1, 1)),
+        (date(2024, 1, 1), pl.Datetime("ms"), datetime(2024, 1, 1)),
+        (date(2024, 1, 1), pl.Datetime("us"), datetime(2024, 1, 1)),
+        (date(2024, 1, 1), pl.Datetime("ns"), datetime(2024, 1, 1)),
+        (
+            date(2024, 1, 1),
+            pl.Datetime("ms", "EST"),
+            datetime(2024, 1, 1, tzinfo=ZoneInfo("EST")),
+        ),
+        (datetime(2024, 1, 1), pl.Date, date(2024, 1, 1)),
+        (datetime(2024, 1, 1), pl.Datetime, datetime(2024, 1, 1)),
+        (datetime(2024, 1, 1), pl.Datetime("ms"), datetime(2024, 1, 1)),
+        (datetime(2024, 1, 1), pl.Datetime("us"), datetime(2024, 1, 1)),
+        (datetime(2024, 1, 1), pl.Datetime("ns"), datetime(2024, 1, 1)),
+        (
+            datetime(2024, 1, 1, tzinfo=ZoneInfo("EST")),
+            pl.Datetime("ms", "EST"),
+            datetime(2024, 1, 1, tzinfo=ZoneInfo("EST")),
+        ),
+    ],
+    ids=[
+        "date to date",
+        "date to datetime",
+        "date to datetime('ms')",
+        "date to datetime('us')",
+        "date to datetime('ns')",
+        "date to datetime('ms', 'EST')",
+        "datetime to date",
+        "datetime to datetime",
+        "datetime to datetime('ms')",
+        "datetime to datetime('us')",
+        "datetime to datetime('ns')",
+        "datetime(tz=EST) to datetime('ms', 'EST')",
+    ],
+)
+def test_literal(value_in, dtype, expected_value) -> None:
+    out = pl.select(pl.lit(value_in, dtype))
+    assert out.schema == OrderedDict({"literal": dtype})
+    assert out.item() == expected_value