issues: 545764524

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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
545764524 MDU6SXNzdWU1NDU3NjQ1MjQ= 3665 Cannot roundtrip time in NETCDF4_CLASSIC 10194086 closed 0     4 2020-01-06T14:47:48Z 2020-01-16T18:27:15Z 2020-01-16T18:27:14Z MEMBER      

MCVE Code Sample

``` python import numpy as np import xarray as xr time = xr.cftime_range("2006-01-01", periods=2, calendar="360_day")

da = xr.DataArray(time, dims=["time"]) da.encoding["dtype"] = np.float da.to_netcdf("tst.nc", format="NETCDF4_CLASSIC")

ds = xr.open_dataset("tst.nc") ds.to_netcdf("tst2.nc", format="NETCDF4_CLASSIC") ```

yields: python ValueError: could not safely cast array from dtype int64 to int32

Or an example without to_netcdf:

```python import numpy as np import xarray as xr

time = xr.cftime_range("2006-01-01", periods=2, calendar="360_day")

da = xr.DataArray(time, dims=["time"]) da.encoding["_FillValue"] = np.array([np.nan])

xr.backends.netcdf3.encode_nc3_variable(xr.conventions.encode_cf_variable(da)) ```

Expected Output

Xarray can save the dataset/ an xr.Variable.

Problem Description

If there is a time variable that can be encoded using integers only, but that has a _FillValue set to NaN, saving to_netcdf(name, format="NETCDF4_CLASSIC") fails. The problem is that xarray adds a (unnecessary) _FillValue when saving a file.

Note: if the time cannot be encoded using integers only, it works: ``` python da = xr.DataArray(time, dims=["time"]) da.encoding["_FillValue"] = np.array([np.nan]) da.encoding["units"] = "days since 2006-01-01T12:00:00"

xr.backends.netcdf3.encode_nc3_variable(xr.conventions.encode_cf_variable(da))

```

Another note: when saving with NETCDF4 ``` python da = xr.DataArray(time, dims=["time"]) da.encoding["_FillValue"] = np.array([np.nan])

xr.backends.netCDF4_._encode_nc4_variable(xr.conventions.encode_cf_variable(da)) The following is returned: <xarray.Variable (time: 2)> array([0, 1]) Attributes: units: days since 2006-01-01 00:00:00.000000 calendar: proleptic_gregorian _FillValue: [-9223372036854775808] ```

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.7.3 | packaged by conda-forge | (default, Jul 1 2019, 21:52:21) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.12.14-lp151.28.36-default machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.1 xarray: 0.14.1 pandas: 0.25.2 numpy: 1.17.3 scipy: 1.3.1 netCDF4: 1.5.3 pydap: None h5netcdf: 0.7.4 h5py: 2.10.0 Nio: None zarr: None cftime: 1.0.4.2 nc_time_axis: 1.2.0 PseudoNetCDF: None rasterio: 1.1.1 cfgrib: None iris: None bottleneck: 1.3.1 dask: 2.6.0 distributed: 2.6.0 matplotlib: 3.1.2 cartopy: 0.17.0 seaborn: 0.9.0 numbagg: None setuptools: 41.4.0 pip: 19.3.1 conda: None pytest: 5.2.2 IPython: 7.9.0 sphinx: 2.2.1 
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