issues: 296673404

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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
296673404 MDU6SXNzdWUyOTY2NzM0MDQ= 1906 Coordinate attributes as DataArray type doesn't export to netcdf 167802 closed 0     5 2018-02-13T09:48:53Z 2018-02-26T09:34:24Z 2018-02-26T09:34:24Z CONTRIBUTOR      

Code Sample, a copy-pastable example if possible

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

arr = xr.DataArray([[1, 2, 3]], dims=['time', 'x']) arr['time'] = np.array([1]) time_bnds = xr.DataArray([0, 1], dims='time_bounds') arr['time'].attrs['bounds'] = time_bnds

dataset = xr.Dataset({'arr': arr, 'time_bnds': time_bnds})

dataset.to_netcdf('time_bnd.nc') ```

Problem description

This code produces a TypeError Traceback (most recent call last): File "test_time_bounds.py", line 12, in <module> dataset.to_netcdf('time_bnd.nc') File "/home/a001673/.local/lib/python2.7/site-packages/xarray/core/dataset.py", line 1132, in to_netcdf unlimited_dims=unlimited_dims) File "/home/a001673/.local/lib/python2.7/site-packages/xarray/backends/api.py", line 598, in to_netcdf _validate_attrs(dataset) File "/home/a001673/.local/lib/python2.7/site-packages/xarray/backends/api.py", line 121, in _validate_attrs check_attr(k, v) File "/home/a001673/.local/lib/python2.7/site-packages/xarray/backends/api.py", line 112, in check_attr 'files'.format(value)) TypeError: Invalid value for attr: <xarray.DataArray (time_bounds: 2)> array([0, 1]) Dimensions without coordinates: time_bounds must be a number string, ndarray or a list/tuple of numbers/strings for serialization to netCDF files This is a problem for me because we need to provide attributes to the coordinate variables and save the to netcdf in order to be CF compliant. There are workarounds (like saving the time_bnds as a regular variable and putting its name as an attribute of the time variable) , but the provided code seems to be the most intuitive way to do it.

Expected output

I would expect an output like this (ncdump -h): netcdf time_bnd { dimensions: time = 1 ; time_bounds = 2 ; x = 3 ; variables: int64 time(time) ; time:bounds = "time_bnds" ; int64 time_bnds(time_bounds) ; int64 arr(time, x) ;

Output of xr.show_versions()

In [2]: xr.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 2.7.5.final.0 python-bits: 64 OS: Linux OS-release: 3.10.0-693.11.6.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: None.None xarray: 0.10.0 pandas: 0.21.0 numpy: 1.13.3 scipy: 0.18.1 netCDF4: 1.1.8 h5netcdf: 0.4.2 Nio: None bottleneck: 1.2.1 cyordereddict: None dask: 0.16.1 matplotlib: 2.1.0 cartopy: None seaborn: None setuptools: 38.4.0 pip: 9.0.1 conda: None pytest: 3.1.3 IPython: 5.5.0 sphinx: 1.6.6 
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