issues: 154818715

For an item to be a value in a Dataset, it either needs to be array-like, or pass lib.is_scalar.

I think this is probably too strict - I'd propose anything can be a value, and it only gets treated as an array if it looks like one - thoughts?

Here's the code that checks the values: https://github.com/pydata/xarray/blob/master/xarray/core/variable.py#L52

``` python In [13]: class B(object): pass ....:

In [14]: xr.Dataset({'a':B()})

ValueError Traceback (most recent call last) <ipython-input-14-b2eeb6de19ea> in <module>() ----> 1 xr.Dataset({'a':B()})

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/dataset.py in init(self, data_vars, coords, attrs, compat, **kwargs) 207 coords = set() 208 if data_vars is not None or coords is not None: --> 209 self._set_init_vars_and_dims(data_vars, coords, compat) 210 if attrs is not None: 211 self.attrs = attrs

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/dataset.py in _set_init_vars_and_dims(self, vars, coords, compat) 258 aligned = align_variables(variables) 259 new_variables, new_coord_names = expand_variables(aligned, --> 260 compat=compat) 261 262 new_coord_names.update(coords)

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/merge.py in expand_variables(raw_variables, old_variables, compat) 75 add_variable(dim, coord.variable) 76 var = var.variable ---> 77 add_variable(name, var) 78 79 return new_variables, new_coord_names

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/merge.py in add_variable(name, var) 55 56 def add_variable(name, var): ---> 57 var = _as_dataset_variable(name, var) 58 if name not in variables: 59 variables[name] = var

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/merge.py in _as_dataset_variable(name, var) 9 """ 10 try: ---> 11 var = as_variable(var, key=name) 12 except TypeError: 13 raise TypeError('variables must be given by arrays or a tuple of '

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/variable.py in as_variable(obj, key, strict, copy) 55 obj = Variable(obj.name, obj) 56 elif key is not None: ---> 57 obj = Variable(key, obj) 58 else: 59 raise TypeError('cannot infer Variable dimensions')

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/variable.py in init(self, dims, data, attrs, encoding, fastpath) 211 """ 212 self._data = as_compatible_data(data, fastpath=fastpath) --> 213 self._dims = self._parse_dimensions(dims) 214 self._attrs = None 215 self._encoding = None

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/variable.py in _parse_dimensions(self, dims) 319 raise ValueError('dimensions %s must have the same length as the ' 320 'number of data dimensions, ndim=%s' --> 321 % (dims, self.ndim)) 322 return dims 323

ValueError: dimensions ('a',) must have the same length as the number of data dimensions, ndim=0 ```