File "/home/py_user/miniconda2/envs/v0/lib/python2.7/site-packages/xarray/core/dataarray.py", line 1746, in to_netcdf
    return dataset.to_netcdf(*args, **kwargs)
  File "/home/py_user/miniconda2/envs/v0/lib/python2.7/site-packages/xarray/core/dataset.py", line 1254, in to_netcdf
    compute=compute)
  File "/home/py_user/miniconda2/envs/v0/lib/python2.7/site-packages/xarray/backends/api.py", line 724, in to_netcdf
    unlimited_dims=unlimited_dims, compute=compute)
  File "/home/py_user/miniconda2/envs/v0/lib/python2.7/site-packages/xarray/core/dataset.py", line 1181, in dump_to_store
    store.sync(compute=compute)
...
  File "/home/py_user/miniconda2/envs/v0/lib/python2.7/multiprocessing/synchronize.py", line 95, in __getstate__
    assert_spawning(self)
  File "/home/py_user/miniconda2/envs/v0/lib/python2.7/multiprocessing/forking.py", line 52, in assert_spawning
    ' through inheritance' % type(self).__name__