code: def add_edge(graph, vertex_from, vertex_to):
      """
      Add a directed edge to the graph.
      """
      if vertex_from not in graph:
          graph[vertex_from] = []
  
      graph[vertex_from].append(vertex_to)
  
label_desc: Use image node_id 3 for calling a global function with example usage: add_edge(graph, vertex_from, vertex_to) without return types