issues: 538068264

MCVE Code Sample

``` In [1]: import numpy as np; import pandas as pd; import xarray as xr

In [2]: times = pd.date_range('2000', periods=3)

In [3]: da = xr.DataArray(times, dims=['a'], coords=[[1, 2, 3]], name='foo')

In [4]: da.encoding['_FillValue'] = 1.0e20

In [5]: da.encoding['dtype'] = np.dtype('float64')

In [6]: da.to_dataset().to_netcdf('test.nc')

OverflowError Traceback (most recent call last) <ipython-input-6-cbc6b2cfdf9a> in <module> ----> 1 da.to_dataset().to_netcdf('test.nc')

~/Software/xarray/xarray/core/dataset.py in to_netcdf(self, path, mode, format, group, engine, encoding, unlimited_dims, compute, invalid_netcdf) 1548 unlimited_dims=unlimited_dims, 1549 compute=compute, -> 1550 invalid_netcdf=invalid_netcdf, 1551 ) 1552

~/Software/xarray/xarray/backends/api.py in to_netcdf(dataset, path_or_file, mode, format, group, engine, encoding, unlimited_dims, compute, multifile, invalid_netcdf) 1071 # to be parallelized with dask 1072 dump_to_store( -> 1073 dataset, store, writer, encoding=encoding, unlimited_dims=unlimited_dims 1074 ) 1075 if autoclose:

~/Software/xarray/xarray/backends/api.py in dump_to_store(dataset, store, writer, encoder, encoding, unlimited_dims) 1117 variables, attrs = encoder(variables, attrs) 1118 -> 1119 store.store(variables, attrs, check_encoding, writer, unlimited_dims=unlimited_dims) 1120 1121

~/Software/xarray/xarray/backends/common.py in store(self, variables, attributes, check_encoding_set, writer, unlimited_dims) 291 writer = ArrayWriter() 292 --> 293 variables, attributes = self.encode(variables, attributes) 294 295 self.set_attributes(attributes)

~/Software/xarray/xarray/backends/common.py in encode(self, variables, attributes) 380 # All NetCDF files get CF encoded by default, without this attempting 381 # to write times, for example, would fail. --> 382 variables, attributes = cf_encoder(variables, attributes) 383 variables = {k: self.encode_variable(v) for k, v in variables.items()} 384 attributes = {k: self.encode_attribute(v) for k, v in attributes.items()}

~/Software/xarray/xarray/conventions.py in cf_encoder(variables, attributes) 758 _update_bounds_encoding(variables) 759 --> 760 new_vars = {k: encode_cf_variable(v, name=k) for k, v in variables.items()} 761 762 # Remove attrs from bounds variables (issue #2921)

~/Software/xarray/xarray/conventions.py in <dictcomp>(.0) 758 _update_bounds_encoding(variables) 759 --> 760 new_vars = {k: encode_cf_variable(v, name=k) for k, v in variables.items()} 761 762 # Remove attrs from bounds variables (issue #2921)

~/Software/xarray/xarray/conventions.py in encode_cf_variable(var, needs_copy, name) 248 variables.UnsignedIntegerCoder(), 249 ]: --> 250 var = coder.encode(var, name=name) 251 252 # TODO(shoyer): convert all of these to use coders, too:

~/Software/xarray/xarray/coding/variables.py in encode(self, variable, name) 163 if fv is not None: 164 # Ensure _FillValue is cast to same dtype as data's --> 165 encoding["_FillValue"] = data.dtype.type(fv) 166 fill_value = pop_to(encoding, attrs, "_FillValue", name=name) 167 if not pd.isnull(fill_value):

OverflowError: Python int too large to convert to C long ```

Expected Output

I think this should succeed in writing to a netCDF file (it worked in xarray 0.14.0 and earlier).

Problem Description

I think this (admittedly very subtle) issue was introduced in https://github.com/pydata/xarray/pull/3502. Essentially at the time data enters CFMaskCoder.encode it does not necessarily have the dtype it will ultimately be encoded with. In the case of this example, data has type int64, but when it will be stored in the netCDF file it will be a double-precision float.

A possible solution here might be to rely on encoding['dtype'] (if it exists) to determine the type to cast the encoding values for '_FillValue' and 'missing_value' to, instead of relying solely on data.dtype (maybe use that as a fallback).

cc: @spencerahill

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.7.3 | packaged by conda-forge | (default, Dec 6 2019, 08:36:57) [Clang 9.0.0 (tags/RELEASE_900/final)] python-bits: 64 OS: Darwin OS-release: 19.0.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.1 xarray: master pandas: 0.25.3 numpy: 1.17.3 scipy: 1.3.2 netCDF4: 1.5.3 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.0.4.2 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.9.0 distributed: 2.9.0 matplotlib: 3.1.2 cartopy: None seaborn: None numbagg: None setuptools: 42.0.2.post20191203 pip: 19.3.1 conda: None pytest: 5.3.2 IPython: 7.10.1 sphinx: None