code: def ind_nodes(self):
          
          graph = self.graph
  
          dependent_nodes = set(
              node for dependents
              in graph.values() for node in dependents)
          return [node_ for node_ in graph if node_ not in dependent_nodes]
docs: Returns a list of all nodes in the graph with no dependencies.
  
          Returns:
              list: A list of all independent nodes.