class_docstr: interface of Invertible data
code: def inverse_op(self, *args, **kwargs):
      raise NotImplementedError
  
imports: from __future__ import absolute_import, print_function
  from abc import ABCMeta, abstractmethod
  import numpy
  import tensorflow
  from six import with_metaclass
  from niftynet.engine.application_variables import RESTORABLE
label_desc: Use image node_id 1 for calling the Invertible obj's underlying member method code with example usage: obj.inverse_op() without return types