BUG: fix error writing a column with mix of datetimes with and without timezone without arrow

CHANGES.md

@@ -4,6 +4,9 @@
 
 ### Bug fixes
 
+-   Fix error in `write_dataframe` with `use_arrow=False` when writing an object-type
+    column with datetimes without any time zone offsets or with a mix of offsets and
+    no offsets (#634).
 -   Fix writing non-string object columns with arrow (#630).
 -   Fix writing empty string category columns with arrow fails (#621).
 -   Fix Time type columns being skipped with `use_arrow=False` (#617).

pyogrio/_io.pyx

@@ -3070,6 +3070,8 @@ def ogr_write(
                         tz_array = gdal_tz_offsets.get(fields[field_idx], None)
                         if tz_array is None:
                             gdal_tz = 0
+                        elif np.isnan(tz_array[i]):
+                            gdal_tz = 0
                         else:
                             gdal_tz = tz_array[i]
                         OGR_F_SetFieldDateTimeEx(

pyogrio/geopandas.py

@@ -921,7 +921,9 @@ def write_dataframe(
         elif col.dtype == "object":
             # Column of Timestamp/datetime objects, split in naive datetime and tz.
             if pd.api.types.infer_dtype(df[name]) == "datetime":
-                tz_offset = col.map(lambda x: x.utcoffset(), na_action="ignore")
+                tz_offset = col.map(lambda x: x.utcoffset(), na_action="ignore").astype(
+                    "timedelta64[us]" if PANDAS_GE_30 else "timedelta64[ns]"
+                )
                 gdal_offset_repr = tz_offset // pd.Timedelta("15m") + 100
                 gdal_tz_offsets[name] = gdal_offset_repr.values
                 naive = col.map(lambda x: x.replace(tzinfo=None), na_action="ignore")

pyogrio/tests/test_geopandas_io.py

@@ -3,7 +3,7 @@
 import os
 import re
 import warnings
-from datetime import date, datetime, time, timezone
+from datetime import date, datetime, time, timedelta, timezone
 from decimal import Decimal
 from io import BytesIO
 from pathlib import Path
@@ -1005,6 +1005,54 @@ def test_write_read_datetime_tz_mixed_offsets(
         assert_geodataframe_equal(result, df)
 
 
+@pytest.mark.parametrize(
+    "dates",
+    [
+        [
+            datetime(2023, 1, 1, 11, 0, 1, 111000),
+            datetime(2023, 6, 1, 10, 0, 1, 111000),
+            np.nan,
+        ],
+        [
+            datetime(2023, 1, 1, 11, 0, 1, 111000, tzinfo=timezone(timedelta(hours=1))),
+            datetime(2023, 6, 1, 10, 0, 1, 111000),
+            np.nan,
+        ],
+    ],
+)
+@pytest.mark.requires_arrow_write_api
+@pytest.mark.skipif(
+    not GDAL_GE_311,
+    reason="before GDAL 3.11, datetimes weren't handled as well",
+)
+def test_write_read_datetime_tz_offsets_None(tmp_path, dates, use_arrow):
+    """Test writing a column with datetimes with and without time zone offsets."""
+    df = gp.GeoDataFrame(
+        {"dates": dates, "geometry": [Point(1, 1)] * len(dates)},
+        crs="EPSG:4326",
+        dtype=object,
+    )
+    fpath = tmp_path / "test.gpkg"
+    write_dataframe(df, fpath, use_arrow=use_arrow)
+    result = read_dataframe(
+        fpath,
+        use_arrow=use_arrow,
+        datetime_as_string=False,
+        mixed_offsets_as_utc=False,
+    )
+
+    exp_df = df.copy()
+    if dates[0].tzinfo is None:
+        exp_df.dates = pd.to_datetime(exp_df.dates, utc=False)
+        if PANDAS_GE_20:
+            exp_df.dates = exp_df.dates.dt.as_unit("ms")
+
+    if not PANDAS_GE_30:
+        exp_df.loc[2, "dates"] = None
+
+    assert_geodataframe_equal(result, exp_df)
+
+
 @pytest.mark.parametrize("ext", [ext for ext in ALL_EXTS if ext != ".shp"])
 @pytest.mark.parametrize(
     "dates_raw",