issues: 63344028

Currently this raises a strange error:

python import xray import numpy as np ds = xray.Dataset({'a': ('x', [np.nan] * 3)}) ds.fillna({'a': xray.DataArray([1, 2, 3], dims='x')})

```

AttributeError Traceback (most recent call last) /Users/shoyer/miniconda/envs/rapid/lib/python2.7/site-packages/IPython/core/formatters.pyc in call(self, obj) 693 type_pprinters=self.type_printers, 694 deferred_pprinters=self.deferred_printers) --> 695 printer.pretty(obj) 696 printer.flush() 697 return stream.getvalue()

/Users/shoyer/miniconda/envs/rapid/lib/python2.7/site-packages/IPython/lib/pretty.pyc in pretty(self, obj) 399 if callable(meth): 400 return meth(obj, self, cycle) --> 401 return _default_pprint(obj, self, cycle) 402 finally: 403 self.end_group()

/Users/shoyer/miniconda/envs/rapid/lib/python2.7/site-packages/IPython/lib/pretty.pyc in default_pprint(obj, p, cycle) 519 if _safe_getattr(klass, '__repr__', None) not in _baseclass_reprs: 520 # A user-provided repr. Find newlines and replace them with p.break() --> 521 _repr_pprint(obj, p, cycle) 522 return 523 p.begin_group(1, '<')

/Users/shoyer/miniconda/envs/rapid/lib/python2.7/site-packages/IPython/lib/pretty.pyc in repr_pprint(obj, p, cycle) 701 """A pprint that just redirects to the normal repr function.""" 702 # Find newlines and replace them with p.break() --> 703 output = repr(obj) 704 for idx,output_line in enumerate(output.splitlines()): 705 if idx:

/Users/shoyer/dev/xray/xray/core/dataset.pyc in repr(self) 1043 1044 def repr(self): -> 1045 return formatting.dataset_repr(self) 1046 1047 def isel(self, **indexers):

/Users/shoyer/dev/xray/xray/core/formatting.pyc in dataset_repr(ds) 231 232 summary.append(coords_repr(ds.coords, col_width=col_width)) --> 233 summary.append(vars_repr(ds.data_vars, col_width=col_width)) 234 if ds.attrs: 235 summary.append(attrs_repr(ds.attrs))

/Users/shoyer/dev/xray/xray/core/formatting.pyc in _mapping_repr(mapping, title, summarizer, col_width) 170 summary = ['%s:' % title] 171 if mapping: --> 172 summary += [summarizer(k, v, col_width) for k, v in mapping.items()] 173 else: 174 summary += [EMPTY_REPR]

/Users/shoyer/miniconda/envs/rapid/lib/python2.7/_abcoll.pyc in items(self) 412 def items(self): 413 "D.items() -> list of D's (key, value) pairs, as 2-tuples" --> 414 return [(key, self[key]) for key in self] 415 416 def values(self):

/Users/shoyer/dev/xray/xray/core/dataset.pyc in getitem(self, key) 371 def getitem(self, key): 372 if key not in self._dataset._coord_names: --> 373 return self._dataset[key] 374 else: 375 raise KeyError(key)

/Users/shoyer/dev/xray/xray/core/dataset.pyc in getitem(self, key) 751 key = np.asarray(key) 752 if key.ndim == 0: --> 753 return DataArray._new_from_dataset(self, key.item()) 754 else: 755 return self._copy_listed(key)

/Users/shoyer/dev/xray/xray/core/dataarray.pyc in _new_from_dataset(cls, dataset, name) 198 """ 199 obj = object.new(cls) --> 200 obj._dataset = dataset._copy_listed([name], keep_attrs=False) 201 if name not in obj._dataset: 202 # handle virtual variables

/Users/shoyer/dev/xray/xray/core/dataset.pyc in _copy_listed(self, names, keep_attrs) 680 needed_dims = set() 681 for v in variables.values(): --> 682 needed_dims.update(v._dims) 683 for k in self._coord_names: 684 if set(self._variables[k]._dims) <= needed_dims:

AttributeError: 'NotImplementedType' object has no attribute '_dims' ```