class_docstr: Convenience class that makes it easy to share variables.
  Each insance of this class creates its own set of variables, but
  each subsequent execution of an instance will re-use its variables.
  
  Graph components that define variables should inherit from this class
  and implement their logic in the `_build` method.
docstr: Subclasses should implement their logic here.
      
code: def _build(self, *args, **kwargs):
      """Subclasses should implement their logic here."""
      raise NotImplementedError
  
file_path: seq2seq/seq2seq/graph_module.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import tensorflow
label_desc: Use image node_id 2 for calling the GraphModule obj's underlying member method code with example usage: obj._build() without return types