issues: 429572364

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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
429572364 MDU6SXNzdWU0Mjk1NzIzNjQ= 2868 netCDF4: support for structured arrays as attribute values; serialize as "compound types" 167164 open 0     3 2019-04-05T03:54:17Z 2022-04-07T15:23:25Z   NONE      

Code Sample, a copy-pastable example if possible

A "Minimal, Complete and Verifiable Example" will make it much easier for maintainers to help you: http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports

```python ds.attrs = dict(a=dict(b=2)) ds.to_netcdf(outfile)

...

~/miniconda3/envs/ana/lib/python3.6/site-packages/xarray/backends/api.py in check_attr(name, value) 158 'a string, an ndarray or a list/tuple of ' 159 'numbers/strings for serialization to netCDF ' --> 160 'files'.format(value)) 161 162 # Check attrs on the dataset itself

TypeError: Invalid value for attr: {'b': 2} must be a number, a string, an ndarray or a list/tuple of numbers/strings for serialization to netCDF files

```

Problem description

I'm not entirely sure if this should be possible, but it seems like it should be from this email: https://www.unidata.ucar.edu/support/help/MailArchives/netcdf/msg10502.html

Nested attributes would be nice as a way to namespace metadata.

Expected Output

Netcdf with nested global attributes.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.8 |Anaconda, Inc.| (default, Dec 30 2018, 01:22:34) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.18.0-16-lowlatency machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_AU.UTF-8 LOCALE: en_AU.UTF-8 libhdf5: 1.10.4 libnetcdf: 4.6.2 xarray: 0.12.0 pandas: 0.24.2 numpy: 1.16.2 scipy: 1.2.1 netCDF4: 1.4.3.2 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.0.3.4 nc_time_axis: None PseudonetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: None distributed: None matplotlib: 3.0.3 cartopy: 0.17.0 seaborn: None setuptools: 40.8.0 pip: 19.0.3 conda: None pytest: 4.3.1 IPython: 7.3.0 sphinx: None 
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     13221727 issue

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