Given a dataset object and data in the appropriate format for
        the interface, return a simple scalar.

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