old_contents: class Graph(object):
      def __init__(self):
          self.g = {}
  
      def nodes(self):
          pass
  
      def edges(self):
          pass
  
      def add_node(self, n):
          pass
  
      def add_edge(self, n1, n2):
          pass
  
      def del_node(self, n):
          pass
  
      def del_edge(self, n1, n2):
          pass
  
      def has_node(self, n):
          pass
  
      def neighbors(self, n):
          pass
  
      def adjacent(self, n1, n2):
          pass
  
new_contents: class Graph(object):
      def __init__(self):
          self.g = {}
  
      def nodes(self):
          pass
  
      def edges(self):
          pass
  
      def add_node(self, n):
          self.g[n] = []
  
      def add_edge(self, n1, n2):
          self.g[n1] = self.g[n1].append(n2)
  
      def del_node(self, n):
          pass
  
      def del_edge(self, n1, n2):
          pass
  
      def has_node(self, n):
          pass
  
      def neighbors(self, n):
          pass
  
      def adjacent(self, n1, n2):
          pass
  
subject: create add_node and add_edge