issues

I have an issue when saving a Dataset to NetCDF. This is the example NetCDF I am using.

python import xarray as xr d = xr.open_dataset('example.nc') d.to_netcdf('out.nc') Then I get: ```python

TypeError Traceback (most recent call last) <ipython-input-4-baf698f1bf45> in <module> ----> 1 d.to_netcdf('out.nc')

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/core/dataset.py in to_netcdf(self, path, mode, format, group, engine, encoding, unlimited_dims, compute) 1241 engine=engine, encoding=encoding, 1242 unlimited_dims=unlimited_dims, -> 1243 compute=compute) 1244 1245 def to_zarr(self, store=None, mode='w-', synchronizer=None, group=None,

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/backends/api.py in to_netcdf(dataset, path_or_file, mode, format, group, engine, encoding, unlimited_dims, compute, multifile) 747 # to be parallelized with dask 748 dump_to_store(dataset, store, writer, encoding=encoding, --> 749 unlimited_dims=unlimited_dims) 750 if autoclose: 751 store.close()

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/backends/api.py in dump_to_store(dataset, store, writer, encoder, encoding, unlimited_dims) 790 791 store.store(variables, attrs, check_encoding, writer, --> 792 unlimited_dims=unlimited_dims) 793 794

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/backends/common.py in store(self, variables, attributes, check_encoding_set, writer, unlimited_dims) 259 writer = ArrayWriter() 260 --> 261 variables, attributes = self.encode(variables, attributes) 262 263 self.set_attributes(attributes)

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/backends/common.py in encode(self, variables, attributes) 345 # All NetCDF files get CF encoded by default, without this attempting 346 # to write times, for example, would fail. --> 347 variables, attributes = cf_encoder(variables, attributes) 348 variables = OrderedDict([(k, self.encode_variable(v)) 349 for k, v in variables.items()])

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/conventions.py in cf_encoder(variables, attributes) 603 """ 604 new_vars = OrderedDict((k, encode_cf_variable(v, name=k)) --> 605 for k, v in iteritems(variables)) 606 return new_vars, attributes

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/conventions.py in <genexpr>(.0) 603 """ 604 new_vars = OrderedDict((k, encode_cf_variable(v, name=k)) --> 605 for k, v in iteritems(variables)) 606 return new_vars, attributes

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/conventions.py in encode_cf_variable(var, needs_copy, name) 233 variables.CFMaskCoder(), 234 variables.UnsignedIntegerCoder()]: --> 235 var = coder.encode(var, name=name) 236 237 # TODO(shoyer): convert all of these to use coders, too:

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/coding/times.py in encode(self, variable, name) 393 data, 394 encoding.pop('units', None), --> 395 encoding.pop('calendar', None)) 396 safe_setitem(attrs, 'units', units, name=name) 397 safe_setitem(attrs, 'calendar', calendar, name=name)

~/miniconda2/envs/cds/lib/python3.6/site-packages/xarray/coding/times.py in encode_cf_datetime(dates, units, calendar) 363 # an OverflowError is raised if the ref_date is too far away from 364 # dates to be encoded (GH 2272). --> 365 num = (pd.DatetimeIndex(dates.ravel()) - ref_date) / time_delta 366 num = num.values.reshape(dates.shape) 367

~/miniconda2/envs/cds/lib/python3.6/site-packages/pandas/core/indexes/datetimelike.py in sub(self, other) 898 result = self._add_offset(-other) 899 elif isinstance(other, (datetime, np.datetime64)): --> 900 result = self._sub_datelike(other) 901 elif is_integer(other): 902 # This check must come after the check for np.timedelta64

~/miniconda2/envs/cds/lib/python3.6/site-packages/pandas/core/indexes/datetimes.py in _sub_datelike(self, other) 876 # require tz compat 877 elif not self._has_same_tz(other): --> 878 raise TypeError("Timestamp subtraction must have the same " 879 "timezones or no timezones") 880 else:

TypeError: Timestamp subtraction must have the same timezones or no timezones ```

I have tried with Python 3.7 and 3.6. I have also installed the latest version of xarray hoping that this issue was linked with #2630. Apparently, with other similar NetCDFs I don't get the error but however this is not supposed to happen, given that the same exact code was working a couple of months ago.