fix(rust, python): raise if tz_localize called on UTC-aware (pola-rs#…

…6526)

Co-authored-by: MarcoGorelli <>

polars/polars-lazy/polars-plan/src/dsl/function_expr/datetime.rs

@@ -145,14 +145,14 @@ pub(super) fn cast_timezone(s: &Series, tz: &str) -> PolarsResult<Series> {
 #[cfg(feature = "timezones")]
 pub(super) fn tz_localize(s: &Series, tz: &str) -> PolarsResult<Series> {
     let ca = s.datetime()?.clone();
-    match ca.time_zone() {
-        Some(tz) if tz == "UTC" => {
-           Ok(ca.with_time_zone(Some("UTC".into()))?.into_series())
-        }
-        Some(tz) if !tz.is_empty() => {
+    match (ca.time_zone(), tz) {
+        (Some(old_tz), _) if !old_tz.is_empty() => {
             Err(PolarsError::ComputeError("Cannot localize a tz-aware datetime. Consider using 'dt.with_time_zone' or 'dt.cast_time_zone'".into()))
         },
-        _ => {
+        (_, "UTC") => {
+           Ok(ca.with_time_zone(Some("UTC".into()))?.into_series())
+        }
+        (_, _) => {
             Ok(ca.with_time_zone(Some("UTC".to_string()))?.cast_time_zone(tz)?.into_series())
         }
     }

py-polars/tests/unit/test_datelike.py

@@ -2178,6 +2178,21 @@ def test_tz_localize() -> None:
     }
 
 
+@pytest.mark.parametrize("time_zone", ["UTC", "Africa/Abidjan"])
+def test_tz_localize_from_utc(time_zone: str) -> None:
+    ts_utc = (
+        pl.Series(["2018-10-28"]).str.strptime(pl.Datetime).dt.tz_localize(time_zone)
+    )
+    with pytest.raises(
+        ComputeError,
+        match=(
+            "^Cannot localize a tz-aware datetime. Consider using "
+            "'dt.with_time_zone' or 'dt.cast_time_zone'$"
+        ),
+    ):
+        ts_utc.dt.tz_localize("America/Maceio")
+
+
 def test_tz_aware_truncate() -> None:
     test = pl.DataFrame(
         {