Loop linked list

# Python program to detect loop 
# in the linked list 
   
# Node class  
class Node: 
   
    # Constructor to initialize 
    # the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
   
class LinkedList: 
   
    # Function to initialize head 
    def __init__(self): 
        self.head = None
   
    # Function to insert a new 
    # node at the beginning 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node 
   
    # Utility function to print it 
    # the linked LinkedList 
    def printList(self): 
        temp = self.head 
        while(temp): 
            print (temp.data, end =" ") 
            temp = temp.next
   
   
    def detectLoop(self): 
         s = set() 
         temp = self.head 
         while (temp): 
          
             # If we have already has 
             # this node in hashmap it 
             # means their is a cycle 
             # (Because you we encountering 
             # the node second time). 
            if (temp in s): 
                return True
     
            # If we are seeing the node for 
            # the first time, insert it in hash 
            s.add(temp) 
     
            temp = temp.next
          
     
         return False
   
# Driver program for testing 
llist = LinkedList() 
llist.push(20) 
llist.push(4) 
llist.push(15) 
llist.push(10) 
   
# Create a loop for testing 
llist.head.next.next.next.next = llist.head; 
  
if( llist.detectLoop()): 
    print ("Loop found") 
else : 
    print ("No Loop ")