BUG: to_json(orient="table") drops fixed-offset timezone (GH#39537)

doc/source/whatsnew/v3.1.0.rst

@@ -360,6 +360,7 @@ I/O
 - :meth:`HDFStore.put` and :meth:`HDFStore.append` now support storing :class:`Series` and :class:`DataFrame` columns with :class:`PeriodDtype` in both ``"fixed"`` and ``"table"`` formats (:issue:`41978`)
 - Bug in :meth:`DataFrame.__repr__` raising ``TypeError`` for a column with a NumPy structured dtype (e.g. produced by :meth:`DataFrame.from_records` from a structured ``ndarray``) (:issue:`55011`)
 - Bug in :meth:`DataFrame.__repr__` where horizontally truncated output could exceed the terminal width by up to 4 characters (:issue:`32461`)
+- Bug in :meth:`DataFrame.to_json` and :meth:`Series.to_json` with ``orient="table"`` silently dropping the timezone of columns with a fixed-offset timezone (e.g. ``datetime.timezone(timedelta(hours=1))``), so the offset was lost on round-trip through :func:`read_json` (:issue:`39537`)
 - Bug in :meth:`DataFrame.to_stata` raising ``KeyError`` when column names require renaming and ``convert_dates`` is specified for a different column (:issue:`60536`)
 - Bug in :meth:`DataFrame.to_string` where ``formatters`` dict was applied to wrong columns when output was horizontally truncated via ``max_cols`` (:issue:`35410`)
 - Fixed :func:`read_json` with ``lines=True`` and ``nrows=0`` to return an empty DataFrame (:issue:`64025`)

pandas/io/json/_table_schema.py

@@ -6,6 +6,7 @@
 
 from __future__ import annotations
 
+from datetime import timezone
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -149,6 +150,10 @@ def convert_pandas_type_to_json_field(arr) -> dict[str, JSONSerializable]:
             zone = timezones.get_timezone(dtype.tz)
             if isinstance(zone, str):
                 field["tz"] = zone
+            elif isinstance(zone, timezone):
+                # fixed-offset stdlib timezone, e.g. timezone(timedelta(hours=1));
+                # str gives a round-trippable "UTC+HH:MM" (GH#39537)
+                field["tz"] = str(zone)
     elif isinstance(dtype, ExtensionDtype):
         field["extDtype"] = dtype.name
     return field

pandas/tests/io/json/test_json_table_schema.py

@@ -1,6 +1,10 @@
 """Tests for Table Schema integration."""
 
 from collections import OrderedDict
+from datetime import (
+    timedelta,
+    timezone,
+)
 from io import StringIO
 import json
 
@@ -499,6 +503,23 @@ def test_convert_pandas_type_to_json_field_datetime(
         expected.update(extra_exp)
         assert result == expected
 
+    @pytest.mark.parametrize(
+        "offset,expected_tz",
+        [
+            (timedelta(hours=1), "UTC+01:00"),
+            (timedelta(hours=-5, minutes=-30), "UTC-05:30"),
+        ],
+    )
+    def test_convert_pandas_type_to_json_field_fixed_offset(self, offset, expected_tz):
+        # GH#39537 fixed-offset stdlib timezones were silently dropped from the
+        # schema instead of being serialized as a round-trippable "UTC+HH:MM"
+        data = pd.Series(
+            pd.to_datetime([1.0], utc=True).tz_convert(timezone(offset)),
+            name="values",
+        )
+        result = convert_pandas_type_to_json_field(data)
+        assert result == {"name": "values", "type": "datetime", "tz": expected_tz}
+
     def test_convert_pandas_type_to_json_period_range(self):
         arr = pd.period_range("2016", freq="Y-DEC", periods=4)
         result = convert_pandas_type_to_json_field(arr)
@@ -708,6 +729,15 @@ class TestTableOrientReader:
                     "2016-01-01", freq="D", periods=4, tz="US/Central", unit="ns"
                 )  # added in # GH 35973
             },
+            {
+                "fixed_offset": pd.date_range(
+                    "2016-01-01",
+                    freq="D",
+                    periods=4,
+                    tz=timezone(timedelta(hours=1)),
+                    unit="ns",
+                )  # GH#39537
+            },
         ],
     )
     def test_read_json_table_orient(self, index_nm, vals):