fix(rust, python): determine supertype of datetimes with timezones an… (

#5240)

polars/polars-core/src/utils/supertype.rs

@@ -244,7 +244,11 @@ pub fn get_supertype(l: &DataType, r: &DataType) -> Option<DataType> {
             // None and Some("<tz>") timezones
             // we cast from more precision to higher precision as that always fits with occasional loss of precision
             #[cfg(feature = "dtype-datetime")]
-            (Datetime(tu_l, tz_l), Datetime(tu_r, tz_r)) if tz_l.is_none() && tz_r.is_some() => {
+            (Datetime(tu_l, tz_l), Datetime(tu_r, tz_r)) if
+                // both are none
+                tz_l.is_none() && tz_r.is_some()
+                // both have the same time zone
+                || (tz_l.is_some() && (tz_l == tz_r)) => {
                 let tu = get_time_units(tu_l, tu_r);
                 Some(Datetime(tu, tz_r.clone()))
             }

py-polars/tests/unit/test_queries.py

@@ -1,8 +1,9 @@
 from __future__ import annotations
 
-from datetime import datetime
+from datetime import datetime, timedelta
 
 import numpy as np
+import pandas as pd
 
 import polars as pl
 
@@ -392,3 +393,24 @@ def test_none_comparison_4773() -> None:
     ).filter(pl.col("x") != pl.col("y"))
     assert df.shape == (3, 2)
     assert df.rows() == [(0, 1), (1, 2), (2, 3)]
+
+
+def test_datetime_supertype_5236() -> None:
+    df = pd.DataFrame(
+        {
+            "StartDateTime": [
+                pd.Timestamp(datetime.utcnow(), tz="UTC"),
+                pd.Timestamp(datetime.utcnow(), tz="UTC"),
+            ],
+            "EndDateTime": [
+                pd.Timestamp(datetime.utcnow(), tz="UTC"),
+                pd.Timestamp(datetime.utcnow(), tz="UTC"),
+            ],
+        }
+    )
+    out = pl.from_pandas(df).filter(
+        pl.col("StartDateTime")
+        < (pl.col("EndDateTime").dt.truncate("1d").max() - timedelta(days=1))
+    )
+    assert out.shape == (0, 2)
+    assert out.dtypes == [pl.Datetime("ns", "UTC")] * 2