fix(python): Convert date and datetime in literal construction

py-polars/polars/functions/lit.py

@@ -78,25 +78,42 @@ 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)
+
+        # parse time unit
         if dtype is not None and (tu := getattr(dtype, "time_unit", "us")) is not None:
             time_unit = tu  # type: ignore[assignment]
         else:
             time_unit = "us"
 
-        time_zone: str | None = getattr(dtype, "time_zone", None)
-        if (tzinfo := value.tzinfo) is not None:
-            tzinfo_str = str(tzinfo)
-            if time_zone is not None and time_zone != tzinfo_str:
-                msg = f"time zone of dtype ({time_zone!r}) differs from time zone of value ({tzinfo!r})"
+        # parse time zone
+        dtype_tz = getattr(dtype, "time_zone", None)
+        value_tz = value.tzinfo
+        if value_tz is None:
+            tz = dtype_tz
+        else:
+            if dtype_tz is None:
+                # value has time zone, but dtype does not: keep value time zone
+                tz = str(value_tz)
+            elif str(value_tz) == dtype_tz:
+                # dtype and value both have same time zone
+                tz = str(value_tz)
+            else:
+                # value has time zone that differs from dtype time zone
+                msg = (
+                    f"time zone of dtype ({dtype_tz!r}) differs from time zone of "
+                    f"value ({value_tz!r})"
+                )
                 raise TypeError(msg)
-            time_zone = tzinfo_str
 
         dt_utc = value.replace(tzinfo=timezone.utc)
         dt_int = datetime_to_int(dt_utc, time_unit)
         expr = lit(dt_int).cast(Datetime(time_unit))
-        if time_zone is not None:
+        if tz is not None:
             expr = expr.dt.replace_time_zone(
-                time_zone, ambiguous="earliest" if value.fold == 0 else "latest"
+                tz, ambiguous="earliest" if value.fold == 0 else "latest"
             )
         return expr
 
@@ -114,8 +131,17 @@ 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

py-polars/tests/unit/operations/namespaces/temporal/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
 
@@ -15,7 +16,7 @@
 if TYPE_CHECKING:
     from zoneinfo import ZoneInfo
 
-    from polars._typing import TemporalLiteral, TimeUnit
+    from polars._typing import PolarsDataType, TemporalLiteral, TimeUnit
 else:
     from polars._utils.convert import string_to_zoneinfo as ZoneInfo
 
@@ -1350,3 +1351,79 @@ def test_dt_mean_deprecated() -> None:
     with pytest.deprecated_call():
         result = s.dt.mean()
     assert result == s.mean()
+
+
+@pytest.mark.parametrize(
+    "dtype",
+    [
+        pl.Date,
+        pl.Datetime("ms"),
+        pl.Datetime("ms", "EST"),
+        pl.Datetime("us"),
+        pl.Datetime("us", "EST"),
+        pl.Datetime("ns"),
+        pl.Datetime("ns", "EST"),
+    ],
+)
+@pytest.mark.parametrize(
+    "value",
+    [
+        date(1677, 9, 22),
+        date(1970, 1, 1),
+        date(2024, 2, 29),
+        date(2262, 4, 11),
+    ],
+)
+def test_literal_from_date(
+    value: date,
+    dtype: PolarsDataType,
+) -> None:
+    out = pl.select(pl.lit(value, dtype=dtype))
+    assert out.schema == OrderedDict({"literal": dtype})
+    if dtype == pl.Datetime:
+        tz = ZoneInfo(dtype.time_zone) if dtype.time_zone is not None else None  # type: ignore[union-attr]
+        value = datetime(value.year, value.month, value.day, tzinfo=tz)
+    assert out.item() == value
+
+
+@pytest.mark.parametrize(
+    "dtype",
+    [
+        pl.Date,
+        pl.Datetime("ms"),
+        pl.Datetime("ms", "EST"),
+        pl.Datetime("us"),
+        pl.Datetime("us", "EST"),
+        pl.Datetime("ns"),
+        pl.Datetime("ns", "EST"),
+    ],
+)
+@pytest.mark.parametrize(
+    "value",
+    [
+        datetime(1677, 9, 22),
+        datetime(1677, 9, 22, tzinfo=ZoneInfo("EST")),
+        datetime(1970, 1, 1),
+        datetime(1970, 1, 1, tzinfo=ZoneInfo("EST")),
+        datetime(2024, 2, 29),
+        datetime(2024, 2, 29, tzinfo=ZoneInfo("EST")),
+        datetime(2262, 4, 11),
+        datetime(2262, 4, 11, tzinfo=ZoneInfo("EST")),
+    ],
+)
+def test_literal_from_datetime(
+    value: datetime,
+    dtype: pl.Date | pl.Datetime,
+) -> None:
+    out = pl.select(pl.lit(value, dtype=dtype))
+    if dtype == pl.Date:
+        value = value.date()  # type: ignore[assignment]
+    elif dtype.time_zone is None and value.tzinfo is not None:  # type: ignore[union-attr]
+        # update the dtype with the supplied time zone in the value
+        dtype = pl.Datetime(dtype.time_unit, str(value.tzinfo))  # type: ignore[union-attr]
+    elif dtype.time_zone is not None and value.tzinfo is None:  # type: ignore[union-attr]
+        # cast from dt without tz to dtype with tz
+        value = value.replace(tzinfo=ZoneInfo(dtype.time_zone))  # type: ignore[union-attr]
+
+    assert out.schema == OrderedDict({"literal": dtype})
+    assert out.item() == value