How to check if search problem has no solution in depth limit search?

Depth-limited search can be terminated with two Conditions of failure:


Standard Failure: it indicates that the problem does not have any solutions.


Cutoff Failure Value: It defines no solution for the problem within a given depth limit.


https://www.analyticsvidhya.com/blog/2021/02/uninformed-search-algorithms-in-ai/


https://www.javatpoint.com/ai-uninformed-search-algorithms


I checked for cut off failure. But I don't know how to check for standard failure. Can you guide me a bit?

Code:

# Python dictionary to act as an adjacency list

graph = {

  '7' : ['19','21', '14'],

  '19': ['1', '12', '31'],

  '21': [],

  '14': ['23', '6'],

  '1' : [],

  '12': [],

  '31': [],

  '23': [],

  '6' : []

}


goal='6'

visited = [] # List of visited nodes of graph.

def dls(visited, graph, node,depth):

   if(depth>=0):

       

       



       if node not in visited:

           visited.append(node)

       

       if(node==goal):

           print("goal found")

           print("path to goal=",visited)

           exit()



       for neighbor in graph[node]:

           dls(visited, graph, neighbor,depth-1)

       


       print(node)


# Driver Code

print("Following is the Depth-First Search")

res=dls(visited, graph, '7',1)

if(res):

   print("Path to goal node available")

   print("Path",path)

else:

   print("No path available for the goal node in given depth limit ie cut off failure")


print("visited=",visited)