html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/3673#issuecomment-579740185,https://api.github.com/repos/pydata/xarray/issues/3673,579740185,MDEyOklzc3VlQ29tbWVudDU3OTc0MDE4NQ==,6628425,2020-01-29T12:47:04Z,2020-01-29T12:47:04Z,MEMBER,Thanks for the fixes @TomAugspurger!,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,547012915
https://github.com/pydata/xarray/issues/3673#issuecomment-573416265,https://api.github.com/repos/pydata/xarray/issues/3673,573416265,MDEyOklzc3VlQ29tbWVudDU3MzQxNjI2NQ==,6628425,2020-01-12T13:38:26Z,2020-01-12T13:38:26Z,MEMBER,"So there are two classes of failures here:

1. With pandas master, adding a CFTimeIndex to a TimedeltaIndex no longer returns a CFTimeIndex; instead it returns a generic Index of cftime objects.

<details><summary>Failure</summary>

<p>

```
2020-01-07T19:19:39.0297443Z =================================== FAILURES ===================================
2020-01-07T19:19:39.0495451Z _________________ test_timedeltaindex_add_cftimeindex[365_day] _________________
2020-01-07T19:19:39.0496702Z 
2020-01-07T19:19:39.0498391Z calendar = '365_day'
2020-01-07T19:19:39.0499052Z 
2020-01-07T19:19:39.0500036Z     @requires_cftime
2020-01-07T19:19:39.0500669Z     @pytest.mark.parametrize(""calendar"", _CFTIME_CALENDARS)
2020-01-07T19:19:39.0501986Z     def test_timedeltaindex_add_cftimeindex(calendar):
2020-01-07T19:19:39.0502556Z         a = xr.cftime_range(""2000"", periods=5, calendar=calendar)
2020-01-07T19:19:39.0503384Z         deltas = pd.TimedeltaIndex([timedelta(days=2) for _ in range(5)])
2020-01-07T19:19:39.0503635Z         result = deltas + a
2020-01-07T19:19:39.0504330Z         expected = a.shift(2, ""D"")
2020-01-07T19:19:39.0505283Z         assert result.equals(expected)
2020-01-07T19:19:39.0506265Z >       assert isinstance(result, CFTimeIndex)
2020-01-07T19:19:39.0507151Z E       AssertionError: assert False
2020-01-07T19:19:39.0508329Z E        +  where False = isinstance(Index([2000-01-03 00:00:00, 2000-01-04 00:00:00, 2000-01-05 00:00:00,\n       2000-01-06 00:00:00, 2000-01-07 00:00:00],\n      dtype='object'), CFTimeIndex)
```

</p>

</details>

2. With pandas master, casting a DatetimeIndex (i.e. the result of a call to `to_datetime`) to an array now returns a NumPy array of timezone-aware `Timestamp` objects, rather than timezone-naive NumPy array of dtype `datetime64[ns]`.
<details><summary>Failure</summary>

<p>

```
2020-01-07T19:19:39.0552973Z ____ test_cf_datetime_nan[num_dates1-days since 2000-01-01-expected_list1] _____
2020-01-07T19:19:39.0553281Z 
2020-01-07T19:19:39.0553765Z num_dates = [nan, 0], units = 'days since 2000-01-01'
2020-01-07T19:19:39.0554887Z expected_list = ['NaT', '2000-01-01T00:00:00Z']
2020-01-07T19:19:39.0555104Z 
2020-01-07T19:19:39.0555251Z     @arm_xfail
2020-01-07T19:19:39.0555406Z     @requires_cftime
2020-01-07T19:19:39.0555551Z     @pytest.mark.parametrize(
2020-01-07T19:19:39.0555693Z         [""num_dates"", ""units"", ""expected_list""],
2020-01-07T19:19:39.0555849Z         [
2020-01-07T19:19:39.0556225Z             ([np.nan], ""days since 2000-01-01"", [""NaT""]),
2020-01-07T19:19:39.0556674Z             ([np.nan, 0], ""days since 2000-01-01"", [""NaT"", ""2000-01-01T00:00:00Z""]),
2020-01-07T19:19:39.0556881Z             (
2020-01-07T19:19:39.0557026Z                 [np.nan, 0, 1],
2020-01-07T19:19:39.0557374Z                 ""days since 2000-01-01"",
2020-01-07T19:19:39.0558208Z                 [""NaT"", ""2000-01-01T00:00:00Z"", ""2000-01-02T00:00:00Z""],
2020-01-07T19:19:39.0558355Z             ),
2020-01-07T19:19:39.0558466Z         ],
2020-01-07T19:19:39.0558591Z     )
2020-01-07T19:19:39.0559984Z     def test_cf_datetime_nan(num_dates, units, expected_list):
2020-01-07T19:19:39.0560153Z         with warnings.catch_warnings():
2020-01-07T19:19:39.0560559Z             warnings.filterwarnings(""ignore"", ""All-NaN"")
2020-01-07T19:19:39.0560733Z             actual = coding.times.decode_cf_datetime(num_dates, units)
2020-01-07T19:19:39.0561076Z         # use pandas because numpy will deprecate timezone-aware conversions
2020-01-07T19:19:39.0561235Z         expected = pd.to_datetime(expected_list)
2020-01-07T19:19:39.0561532Z >       assert_array_equal(expected, actual)
2020-01-07T19:19:39.0561669Z E       AssertionError: 
2020-01-07T19:19:39.0561785Z E       Arrays are not equal
2020-01-07T19:19:39.0561899Z E       
2020-01-07T19:19:39.0562138Z E       Mismatched elements: 2 / 2 (100%)
2020-01-07T19:19:39.0562505Z E        x: array([NaT, Timestamp('2000-01-01 00:00:00+0000', tz='UTC')], dtype=object)
2020-01-07T19:19:39.0563375Z E        y: array([                          'NaT', '2000-01-01T00:00:00.000000000'],
2020-01-07T19:19:39.0563710Z E             dtype='datetime64[ns]')
2020-01-07T19:19:39.0564285Z 
2020-01-07T19:19:39.0564914Z xarray/tests/test_coding_times.py:455: AssertionError
```

</p>

</details>

(2) is simple.  Basically due to a planned change<sup>1</sup> in pandas, the test needs to be edited.  In xarray we still expect `decode_cf_datetime` to return timezone-naive dates.  Therefore we need to make sure that we are comparing against a timezone-naive reference.  

(1) is trickier; I'm not sure if it's something we should raise in the pandas issue tracker.  Essentially we rely on `TimedeltaIndex.__add__(other)` to return `NotImplemented` when `other` is a `CFTimeIndex`; this way it will resort to using `CFTimeIndex.__radd__` instead.  It looks like recent code changes in pandas broke this.

------

<sup>1</sup>See this FutureWarning:
```
FutureWarning: Converting timezone-aware DatetimeArray to timezone-naive ndarray with 'datetime64[ns]' dtype. In the future, this will return an ndarray with 'object' dtype where each element is a 'pandas.Timestamp' with the correct 'tz'.
	To accept the future behavior, pass 'dtype=object'.
	To keep the old behavior, pass 'dtype=""datetime64[ns]""'.
  exec(code_obj, self.user_global_ns, self.user_ns)
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,547012915