Code to find the middle node in the linked list in single traversal in python.

middleLL.py

# program to find the middle node of the Linked List in single traversal

class LinkedList:
    def __init__(self):
        self.head = None

    # returns true is LinkedList is Empty
    def isEmpty(self):
        if self.head is None:
            return True
        else:
            return False

    # method adds elements to the left of the Linked List
    def addToStart(self, data):
        # create a temporary node
        tempNode = Node(data)
        tempNode.setLink(self.head)
        self.head = tempNode
        del tempNode

    # method adds elements to the right of the Linked List
    def addToEnd(self, data):
        start = self.head
        tempNode = Node(data)
        while start.getNextNode():
            start = start.getNextNode()
        start.setLink(tempNode)
        del tempNode
        return True

    # method displays Linked List
    def display(self):
        start = self.head
        if start is None:
            print("Empty List!!!")
            return False
			
        while start:
            print(str(start.getData()), end=" ")
            start = start.link
            if start:
                print("-->", end=" ")
        print()

    # method that returns the middle node of the list
    def middleNode(self):
        start = self.head
        slow = self.head
        fast = self.head
        while True:
            if fast.getNextNode():
                fast = fast.getNextNode()
                slow = slow.getNextNode()
            else:
                break
            if fast.getNextNode():
                fast = fast.getNextNode()
            else:
                break

        return slow.getData()


# node class
class Node:
    # default value of data and link is none if no data is passed
    def __init__(self, data=None, link=None):
        self.data = data
        self.link = link

    # method to update the data feild of Node
    def updateData(self, data):
        self.data = data

    # method to set Link feild the Node
    def setLink(self, node):
        self.link = node

    # method returns data feild of the Node
    def getData(self):
        return self.data

    # method returns address of the next Node
    def getNextNode(self):
        return self.link


# main method
# creating LinkedList
myList = LinkedList()

# adding some elements to the start of LinkedList
myList.addToStart(23)
myList.addToStart(1)
myList.addToStart(5)
myList.addToStart(26)
myList.addToStart(27)
myList.addToStart(28)
# adding some elements to the End of the LinkedList
myList.addToEnd(24)
myList.addToEnd(22)
myList.addToEnd(13)

print("The Elements of the Linked List are : ")
myList.display()

print("\nThe middle Element of the Linked List is : " + str(myList.middleNode()))

'''

The Elements of the Linked List are :
28 --> 27 --> 26 --> 5 --> 1 --> 23 --> 24 --> 22 --> 13

The middle Element of the Linked List is : 1

'''