code: def __str__(self):
      return self.to_string()
  
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 4 for calling the Layer obj's underlying member method code with example usage: obj.__str__() and returns: self