First duplicate element of a linked list in python

Python program for First duplicate element of a linked list. Here more information.

#  Python 3 program for
#  Find the first duplicate element in the linked list

#  Linked list node
class LinkNode :
	def __init__(self, data) :
		self.data = data
		self.next = None
	

class SingleLL :
	def __init__(self) :
		self.head = None
		self.tail = None
	
	def insert(self, data) :
		node = LinkNode(data)
		if (self.head == None) :
			#  Add first node
			self.head = node
		else :
			#  Add node at the end position
			self.tail.next = node
		
		#  New last node
		self.tail = node
	
	#  Display linked list element
	def display(self) :
		if (self.head == None) :
			return
		
		temp = self.head
		#  iterating linked list elements
		while (temp != None) :
			print("", temp.data , end = " →")
			#  Visit to next node
			temp = temp.next
		
		print(" NULL")
	
	#  Find first repeating element 
	#  from front to end in a linked list
	#  Solution are takes O(n*n) time
	def firstDuplicate(self) :
		print()
		#  Display linked list elements
		self.display()
		#  Define some auxiliary variables
		outer = self.head
		inner = None
		result = None
		#  iterating linked list elements
		while (outer != None and result == None) :
			#  Get next node
			inner = outer.next
			#  iterating linked list elements 
			#  from current node to end
			while (inner != None and result == None) :
				if (inner.data == outer.data) :
					#  When get first duplicate node exist
					result = outer
				
				inner = inner.next
			
			#  Visit to next node
			outer = outer.next
		
		if (result == None) :
			print(" First duplicate : None")
		else :
			print(" First duplicate : ", result.data)
		
	

def main() :
	list1 = SingleLL()
	list2 = SingleLL()
	list3 = SingleLL()
	#  Add node in first linked list
	list1.insert(6)
	list1.insert(4)
	list1.insert(5)
	list1.insert(9)
	list1.insert(3)
	list1.insert(5)
	list1.insert(4)
	list1.insert(9)
	#  Add node in second linked list
	list2.insert(6)
	list2.insert(2)
	list2.insert(3)
	list2.insert(3)
	list2.insert(2)
	list2.insert(5)
	list2.insert(3)
	#  Add node in third linked list
	list3.insert(2)
	list3.insert(1)
	list3.insert(8)
	list3.insert(4)
	#  Test
	list1.firstDuplicate()
	list2.firstDuplicate()
	list3.firstDuplicate()

if __name__ == "__main__": main()

Output

 6 → 4 → 5 → 9 → 3 → 5 → 4 → 9 → NULL
 First duplicate :  4

 6 → 2 → 3 → 3 → 2 → 5 → 3 → NULL
 First duplicate :  2

 2 → 1 → 8 → 4 → NULL
 First duplicate : None