old_contents: #!/usr/bin/python
  
  # Author: OMKAR PATHAK
  
  # We can use Python's dictionary for constructing the graph.
  
  
  class AdjacencyList:
      def __init__(self):
          self.List = {}
  
      def addEdge(self, fromVertex, toVertex):
          # check if vertex is already present
          if fromVertex in self.List.keys():
              self.List[fromVertex].append(toVertex)
          else:
              self.List[fromVertex] = [toVertex]
  
      def printList(self):
          for i in self.List:
              print((i, "->", " -> ".join([str(j) for j in self.List[i]])))
  
  
  if __name__ == "__main__":
      al = AdjacencyList()
      al.addEdge(0, 1)
      al.addEdge(0, 4)
      al.addEdge(4, 1)
      al.addEdge(4, 3)
      al.addEdge(1, 0)
      al.addEdge(1, 4)
      al.addEdge(1, 3)
      al.addEdge(1, 2)
      al.addEdge(2, 3)
      al.addEdge(3, 4)
  
      al.printList()
  
      # OUTPUT:
      # 0 -> 1 -> 4
      # 1 -> 0 -> 4 -> 3 -> 2
      # 2 -> 3
      # 3 -> 4
      # 4 -> 1 -> 3
  
new_contents: #!/usr/bin/python
  
  # Author: OMKAR PATHAK
  
  # We can use Python's dictionary for constructing the graph.
  
  
  class AdjacencyList:
      def __init__(self):
          self.adj_list = {}
  
      def add_edge(self, from_vertex: int, to_vertex: int) -> None:
          # check if vertex is already present
          if from_vertex in self.adj_list:
              self.adj_list[from_vertex].append(to_vertex)
          else:
              self.adj_list[from_vertex] = [to_vertex]
  
      def print_list(self) -> None:
          for i in self.adj_list:
              print((i, "->", " -> ".join([str(j) for j in self.adj_list[i]])))
  
  
  if __name__ == "__main__":
      al = AdjacencyList()
      al.add_edge(0, 1)
      al.add_edge(0, 4)
      al.add_edge(4, 1)
      al.add_edge(4, 3)
      al.add_edge(1, 0)
      al.add_edge(1, 4)
      al.add_edge(1, 3)
      al.add_edge(1, 2)
      al.add_edge(2, 3)
      al.add_edge(3, 4)
  
      al.print_list()
  
      # OUTPUT:
      # 0 -> 1 -> 4
      # 1 -> 0 -> 4 -> 3 -> 2
      # 2 -> 3
      # 3 -> 4
      # 4 -> 1 -> 3
  
subject: Update graphs/graph_list.py (#3813)