issues: 798592803

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
798592803 MDU6SXNzdWU3OTg1OTI4MDM= 4853 cftime default's datetime breaks CFTimeIndex 20629530 open 0     4 2021-02-01T18:14:21Z 2021-02-05T18:48:31Z   CONTRIBUTOR      

What happened: With cftime 1.2.0, one can create datetime object with cftime.datetime(*args, calendar='calendar'), instead of using one of the subclasses (ex cftime.DatetimeNoLeap(*args)). In the latest release (1.4.0, yesterday), the subclasses have been deprecated, but kept as legacy. While all xr code still works (it is using the legacy subclasses), the CFTimeIndex object relies on the type of the datetime object in order to infer the calendar. If the datetime was created outside xarray, using the now default constructor, the returned type is not understood and CFTimeIndexbreaks.

What you expected to happen: I expected CFTimeIndex to be independent of the way the datetime object is created.

Minimal Complete Verifiable Example:

```python3 import cftime import numpy as np import xarray as xr

A datetime array, not created in xarray

time = cftime.num2date(np.arange(365), "days since 2000-01-01", calendar="noleap") a = xr.DataArray(np.zeros(365), dims=('time',), coords={'time': time})

a.indexes['time'] Fails with :python3 Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/cftimeindex.py", line 342, in repr attrs_str = format_attrs(self) File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/cftimeindex.py", line 264, in format_attrs attrs["freq"] = f"'{index.freq}'" if len(index) >= 3 else None File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/cftimeindex.py", line 692, in freq return infer_freq(self) File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/frequencies.py", line 96, in infer_freq inferer = _CFTimeFrequencyInferer(index) File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/frequencies.py", line 105, in init self.values = index.asi8 File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/cftimeindex.py", line 673, in asi8 [ File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/coding/cftimeindex.py", line 674, in <listcomp> _total_microseconds(exact_cftime_datetime_difference(epoch, date)) File "/home/phobos/Python/xclim/.tox/py38/lib/python3.8/site-packages/xarray/core/resample_cftime.py", line 370, in exact_cftime_datetime_difference seconds = b.replace(microsecond=0) - a.replace(microsecond=0) File "src/cftime/_cftime.pyx", line 1153, in cftime._cftime.datetime.sub ValueError: cannot compute the time difference between dates with different calendars ``` Anything else we need to know?:

Environment:

Output of <tt>xr.show_versions()</tt> INSTALLED VERSIONS ------------------ commit: None python: 3.8.5 | packaged by conda-forge | (default, Jul 31 2020, 02:39:48) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 5.10.11-arch1-1 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: fr_CA.utf8 LOCALE: fr_CA.UTF-8 libhdf5: 1.12.0 libnetcdf: 4.7.4 xarray: 0.16.2 pandas: 1.2.1 numpy: 1.20.0 scipy: 1.6.0 netCDF4: 1.5.5.1 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.4.0 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.2 dask: 2021.01.1 distributed: None matplotlib: None cartopy: None seaborn: None numbagg: None pint: 0.16.1 setuptools: 46.1.3 pip: 20.1 conda: None pytest: 6.2.2 IPython: 7.19.0 sphinx: None 
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