old_contents: #!/usr/bin/env python
  from __future__ import print_function
  from __future__ import unicode_literals
  
  
  class Graph(object):
      ''' Create an empty graph. '''
      def __init__(self):
          self.graph = {}
          return
  
      def nodes():
          return nodes
  
      def edges():
          return edges
  
      def add_node(self, value):
          self.graph.setdefault(value, [])
          return
  
      def add_edge(self, value1, value2):
          return
  
      def del_node(self, value):
          try:
              del self.graph[value]
          except KeyError:
              raise KeyError('node not in graph')
  
      def has_node(self, value):
          return value in self.graph
  
      def neighbors(self, value):
          return neighbors
  
      def adjecent(self, value, value2):
          return condition
  
new_contents: #!/usr/bin/env python
  from __future__ import print_function
  from __future__ import unicode_literals
  
  
  class Graph(object):
      ''' Create an empty graph. '''
      def __init__(self):
          self.graph = {}
          return
  
      def nodes():
          return nodes
  
      def edges():
          return edges
  
      def add_node(self, value):
          self.graph.setdefault(value, [])
          return
  
      def add_edge(self, value1, value2):
          return
  
      def del_node(self, value):
          try:
              del self.graph[value]
          except KeyError:
              raise KeyError('node not in graph')
  
      def has_node(self, value):
          return value in self.graph
  
      def neighbors(self, value):
          return self.graph[value]
  
      def adjecent(self, value, value2):
          return condition
  
subject: add neighbors function.