code: def __call__(self, *args, **kwargs):
      return self._op(*args, **kwargs)
  
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 3 for calling the Layer obj's underlying member method code with example usage: obj.__call__() and returns: self