code: def build(self):
      self._make_input_layers()
      self._make_output_layers()
      self._get_topological_sort()
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
label_desc: Use image node_id 2 for calling the Graph obj's underlying member method code with example usage: obj.build() without return types