code: def unpack_scalar(cls, dataset, data):
          
          if (len(data.data_vars) == 1 and
              len(data[dataset.vdims[0].name].shape) == 0):
              return data[dataset.vdims[0].name].item()
          return data
docs: Given a dataset object and data in the appropriate format for
          the interface, return a simple scalar.