code: def validate(self, graph):
          
          if not nx.is_directed_acyclic_graph(graph):
              raise DirectedAcyclicGraphInvalid(graph_name=self._name)
docs: Validate the graph by checking whether it is a directed acyclic graph.
  
          Args:
              graph (DiGraph): Reference to a DiGraph object from NetworkX.
  
          Raises:
              DirectedAcyclicGraphInvalid: If the graph is not a valid dag.