enh: support replace_time_zone(None) (#2576)

* enh: support replace_time_zone(None)

* fix typo

Author: MarcoGorelli

narwhals/_duckdb/expr_dt.py

@@ -120,4 +120,13 @@ def truncate(self, every: str) -> DuckDBExpr:
             )
         )
 
+    def replace_time_zone(self, time_zone: str | None) -> DuckDBExpr:
+        if time_zone is None:
+            return self._compliant_expr._with_callable(
+                lambda _input: _input.cast("timestamp")
+            )
+        else:  # pragma: no cover
+            msg = "`replace_time_zone` with non-null `time_zone` not yet implemented for duckdb"
+            raise NotImplementedError(msg)
+
     total_nanoseconds = not_implemented()

narwhals/_ibis/expr_dt.py

@@ -85,6 +85,15 @@ def truncate(self, every: str) -> IbisExpr:
             fn = self._truncate(UNITS_DICT_TRUNCATE[unit])
         return self._compliant_expr._with_callable(fn)
 
+    def replace_time_zone(self, time_zone: str | None) -> IbisExpr:
+        if time_zone is None:
+            return self._compliant_expr._with_callable(
+                lambda _input: _input.cast("timestamp")
+            )
+        else:  # pragma: no cover
+            msg = "`replace_time_zone` with non-null `time_zone` not yet implemented for Ibis"
+            raise NotImplementedError(msg)
+
     nanosecond = not_implemented()
     total_minutes = not_implemented()
     total_seconds = not_implemented()

narwhals/_spark_like/expr_dt.py

@@ -80,3 +80,12 @@ def _truncate(expr: Column) -> Column:
             return self._compliant_expr._F.date_trunc(format, expr)
 
         return self._compliant_expr._with_callable(_truncate)
+
+    def replace_time_zone(self, time_zone: str | None) -> SparkLikeExpr:
+        if time_zone is None:
+            return self._compliant_expr._with_callable(
+                lambda _input: _input.cast("timestamp_ntz")
+            )
+        else:  # pragma: no cover
+            msg = "`replace_time_zone` with non-null `time_zone` not yet implemented for spark-like"
+            raise NotImplementedError(msg)

tests/expr_and_series/dt/replace_time_zone_test.py

@@ -56,7 +56,8 @@ def test_replace_time_zone_none(
         or ("pyarrow_table" in str(constructor) and PYARROW_VERSION < (12,))
     ):
         pytest.skip()
-    if any(x in str(constructor) for x in ("duckdb", "pyspark", "ibis")):
+    if any(x in str(constructor) for x in ("pyspark",)):
+        # pyspark: needs `to_string`
         request.applymarker(pytest.mark.xfail)
     data = {
         "a": [