code: def get_vertices_from_edge_list(graph, edge_list):
      
      node_set = set()
      for edge_id in edge_list:
          edge = graph.get_edge(edge_id)
          a, b = edge['vertices']
          node_set.add(a)
          node_set.add(b)
  
      return list(node_set)
docs: Transforms a list of edges into a list of the nodes those edges connect.
      Returns a list of nodes, or an empty list if given an empty list.