ENH: implement timeszones support for read_json(orient='table') and astype() from 'object'

doc/source/whatsnew/v1.2.0.rst

@@ -120,6 +120,10 @@ Other enhancements
 - ``Styler`` now allows direct CSS class name addition to individual data cells (:issue:`36159`)
 - :meth:`Rolling.mean()` and :meth:`Rolling.sum()` use Kahan summation to calculate the mean to avoid numerical problems (:issue:`10319`, :issue:`11645`, :issue:`13254`, :issue:`32761`, :issue:`36031`)
 - :meth:`DatetimeIndex.searchsorted`, :meth:`TimedeltaIndex.searchsorted`, :meth:`PeriodIndex.searchsorted`, and :meth:`Series.searchsorted` with datetimelike dtypes will now try to cast string arguments (listlike and scalar) to the matching datetimelike type (:issue:`36346`)
+- :meth:`to_json` now implements timezones parsing when orient structure is 'table'.
+- :meth:`read_json` now implements timezones parsing when orient structure is 'table'.
+- :meth:`astype` now attempts to convert to 'datetime64[ns, tz]' directly from 'object' with inferred timezone from string (:issue:`35973`).
+-
 
 .. _whatsnew_120.api_breaking.python:
 

pandas/core/arrays/datetimes.py

@@ -1933,7 +1933,13 @@ def sequence_to_dt64ns(
             data, inferred_tz = objects_to_datetime64ns(
                 data, dayfirst=dayfirst, yearfirst=yearfirst
             )
-            tz = _maybe_infer_tz(tz, inferred_tz)
+            if tz and inferred_tz:
+                #  two timezones: convert to intended from base UTC repr
+                data = tzconversion.tz_convert_from_utc(data.view("i8"), tz)
+                data = data.view(DT64NS_DTYPE)
+            elif inferred_tz:
+                tz = inferred_tz
+
         data_dtype = data.dtype
 
     # `data` may have originally been a Categorical[datetime64[ns, tz]],

pandas/io/json/_json.py

@@ -302,7 +302,9 @@ def __init__(
 
         # NotImplemented on a column MultiIndex
         if obj.ndim == 2 and isinstance(obj.columns, MultiIndex):
-            raise NotImplementedError("orient='table' is not supported for MultiIndex")
+            raise NotImplementedError(
+                "orient='table' is not supported for MultiIndex columns"
+            )
 
         # TODO: Do this timedelta properly in objToJSON.c See GH #15137
         if (

pandas/io/json/_table_schema.py

@@ -323,10 +323,6 @@ def parse_table_schema(json, precise_float):
         for field in table["schema"]["fields"]
     }
 
-    # Cannot directly use as_type with timezone data on object; raise for now
-    if any(str(x).startswith("datetime64[ns, ") for x in dtypes.values()):
-        raise NotImplementedError('table="orient" can not yet read timezone data')
-
     # No ISO constructor for Timedelta as of yet, so need to raise
     if "timedelta64" in dtypes.values():
         raise NotImplementedError(

pandas/tests/frame/methods/test_astype.py

@@ -587,3 +587,27 @@ def test_astype_ignores_errors_for_extension_dtypes(self, df, errors):
             msg = "(Cannot cast)|(could not convert)"
             with pytest.raises((ValueError, TypeError), match=msg):
                 df.astype(float, errors=errors)
+
+    def test_astype_tz_conversion(self):
+        # GH 35973
+        val = {"tz": date_range("2020-08-30", freq="d", periods=2, tz="Europe/London")}
+        expected = DataFrame(val)
+
+        result = expected.astype({"tz": "datetime64[ns, Europe/Berlin]"})
+        expected["tz"] = expected["tz"].dt.tz_convert("Europe/Berlin")
+
+        tm.assert_frame_equal(result, expected)
+
+    @pytest.mark.parametrize("tz", ["UTC", "Europe/Berlin"])
+    def test_astype_tz_object_conversion(self, tz):
+        # GH 35973
+        val = {"tz": date_range("2020-08-30", freq="d", periods=2, tz="Europe/London")}
+        expected = DataFrame(val)
+
+        # convert expected to object dtype from other tz str (independently tested)
+        result = expected.astype({"tz": f"datetime64[ns, {tz}]"})
+        result = result.astype({"tz": "object"})
+
+        # do real test: object dtype to a specified tz, different from construction tz.
+        result = result.astype({"tz": "datetime64[ns, Europe/London]"})
+        tm.assert_frame_equal(result, expected)

pandas/tests/io/json/test_json_table_schema.py

@@ -676,6 +676,11 @@ class TestTableOrientReader:
             {"floats": [1.0, 2.0, 3.0, 4.0]},
             {"floats": [1.1, 2.2, 3.3, 4.4]},
             {"bools": [True, False, False, True]},
+            {
+                "timezones": pd.date_range(
+                    "2016-01-01", freq="d", periods=4, tz="US/Central"
+                )  # added in # GH 35973
+            },
         ],
     )
     @pytest.mark.skipif(sys.version_info[:3] == (3, 7, 0), reason="GH-35309")
@@ -686,22 +691,59 @@ def test_read_json_table_orient(self, index_nm, vals, recwarn):
         tm.assert_frame_equal(df, result)
 
     @pytest.mark.parametrize("index_nm", [None, "idx", "index"])
+    @pytest.mark.parametrize(
+        "vals",
+        [{"timedeltas": pd.timedelta_range("1H", periods=4, freq="T")}],
+    )
+    def test_read_json_table_orient_raises(self, index_nm, vals, recwarn):
+        df = DataFrame(vals, index=pd.Index(range(4), name=index_nm))
+        out = df.to_json(orient="table")
+        with pytest.raises(NotImplementedError, match="can not yet read "):
+            pd.read_json(out, orient="table")
+
+    @pytest.mark.parametrize(
+        "idx",
+        [
+            pd.Index(range(4)),
+            pd.Index(
+                pd.date_range(
+                    "2020-08-30",
+                    freq="d",
+                    periods=4,
+                ),
+                freq=None,
+            ),
+            pd.Index(
+                pd.date_range("2020-08-30", freq="d", periods=4, tz="US/Central"),
+                freq=None,
+            ),
+            pd.MultiIndex.from_product(
+                [
+                    pd.date_range("2020-08-30", freq="d", periods=2, tz="US/Central"),
+                    ["x", "y"],
+                ],
+            ),
+        ],
+    )
     @pytest.mark.parametrize(
         "vals",
         [
-            {"timedeltas": pd.timedelta_range("1H", periods=4, freq="T")},
+            {"floats": [1.1, 2.2, 3.3, 4.4]},
+            {"dates": pd.date_range("2020-08-30", freq="d", periods=4)},
             {
                 "timezones": pd.date_range(
-                    "2016-01-01", freq="d", periods=4, tz="US/Central"
+                    "2020-08-30", freq="d", periods=4, tz="Europe/London"
                 )
             },
         ],
     )
-    def test_read_json_table_orient_raises(self, index_nm, vals, recwarn):
-        df = DataFrame(vals, index=pd.Index(range(4), name=index_nm))
+    @pytest.mark.skipif(sys.version_info[:3] == (3, 7, 0), reason="GH-35309")
+    def test_read_json_table_timezones_orient(self, idx, vals, recwarn):
+        # GH 35973
+        df = DataFrame(vals, index=idx)
         out = df.to_json(orient="table")
-        with pytest.raises(NotImplementedError, match="can not yet read "):
-            pd.read_json(out, orient="table")
+        result = pd.read_json(out, orient="table")
+        tm.assert_frame_equal(df, result)
 
     def test_comprehensive(self):
         df = DataFrame(