class_docstr: Some layers require a one-pass training through the training set
  to determine their internal models, this abstract provides
  interfaces for training these internal models and querying the
  status.
code: def is_ready(self):
      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 2 for calling the DataDependentLayer obj's underlying member method code with example usage: obj.is_ready() without return types