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
246093122,MDU6SXNzdWUyNDYwOTMxMjI=,1494,AssertionError when storing datetime coordinates of wrong units,500246,closed,0,,,2,2017-07-27T16:11:48Z,2019-06-30T04:28:18Z,2019-06-30T04:28:17Z,CONTRIBUTOR,,,,"The following code should probably fail somewhere else than with an `AssertionError` triggered by `to_netcdf`:

```
$ cat mwe.py
#!/usr/bin/env python3.6

import numpy
import xarray

x = xarray.DataArray(
    [1, 2, 3],
    dims=[""X""],
    coords={""X"": numpy.zeros(shape=3, dtype=""M8[ms]"")})

x.to_netcdf(""/tmp/test.nc"")
$ python3.6 mwe.py
Traceback (most recent call last):
  File ""mwe.py"", line 11, in <module>
    x.to_netcdf(""/tmp/test.nc"")
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/core/dataarray.py"", line 1351, in to_netcdf
    dataset.to_netcdf(*args, **kwargs)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/core/dataset.py"", line 977, in to_netcdf
    unlimited_dims=unlimited_dims)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/backends/api.py"", line 573, in to_netcdf
    unlimited_dims=unlimited_dims)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/core/dataset.py"", line 916, in dump_to_store
    unlimited_dims=unlimited_dims)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/backends/common.py"", line 244, in store
    cf_variables, cf_attrs = cf_encoder(variables, attributes)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/conventions.py"", line 1089, in cf_encoder
    for k, v in iteritems(variables))
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/conventions.py"", line 1089, in <genexpr>
    for k, v in iteritems(variables))
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/conventions.py"", line 734, in encode_cf_variable
    var = maybe_encode_datetime(var)
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/conventions.py"", line 585, in maybe_encode_datetime
    data, encoding.pop('units', None), encoding.pop('calendar', None))
  File ""/dev/shm/gerrit/venv/stable-3.6/lib/python3.6/site-packages/xarray/conventions.py"", line 293, in encode_cf_datetime
    assert dates.dtype == 'datetime64[ns]'
AssertionError
```","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/1494/reactions"", ""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue