Python Program For Inserting A Node In A Linked List

# Node class
class Node:

    # Function to initialize the 
    # node object
    def __init__(self, data):

        # Assign data
        self.data = data  
  
        # Initialize next as null
        self.next = None  

# Linked List class
class LinkedList:
  
    # Function to initialize the 
    # Linked List object
    def __init__(self): 
        self.head = None

# This function is in LinkedList class
# Function to insert a new node at 
# the beginning
def push(self, new_data):

    # 1 & 2: Allocate the Node &
    #        Put in the data
    new_node = Node(new_data)
        
    # 3. Make next of new Node as head
    new_node.next = self.head
        
    # 4. Move the head to point to new Node 
    self.head = new_node

# This function is in LinkedList class. 
# Inserts a new node after the given 
# prev_node. This method is defined 
# inside LinkedList class shown above 
def insertAfter(self, prev_node, new_data): 

    # 1. Check if the given prev_node exists 
    if prev_node is None: 
        print "The given previous node must in LinkedList."
        return

    # 2. Create new node & 
    # 3. Put in the data 
    new_node = Node(new_data) 

    # 4. Make next of new Node as next of prev_node 
    new_node.next = prev_node.next

    # 5. make next of prev_node as new_node 
    prev_node.next = new_node 

 # This function is defined in Linked List 
 # class appends a new node at the end.  
 # This method is defined inside LinkedList 
 # class shown above 
 def append(self, new_data):

    # 1. Create a new node
    # 2. Put in the data
    # 3. Set next as None
    new_node = Node(new_data)

    # 4. If the Linked List is empty, then 
    #    make the new node as head
    if self.head is None:
         self.head = new_node
         return

    # 5. Else traverse till the last node
    last = self.head
    while (last.next):
        last = last.next

    # 6. Change the next of last node
    last.next =  new_node

# A complete working Python program to demonstrate all
# insertion methods of linked list

# Node class
class Node:

    # Function to initialize the 
    # node object
    def __init__(self, data):

        # Assign data
        self.data = data  

        # Initialize next as null
        self.next = None  


# Linked List class contains a
# Node object
class LinkedList:

    # Function to initialize head
    def __init__(self):
        self.head = None

    # Functio to insert a new node at
    # the beginning
    def push(self, new_data):

        # 1 & 2: Allocate the Node &
        #        Put in the data
        new_node = Node(new_data)

        # 3. Make next of new Node as head
        new_node.next = self.head

        # 4. Move the head to point to new Node
        self.head = new_node


    # This function is in LinkedList class. 
    # Inserts a new node after the given
    # prev_node. This method is defined 
    # inside LinkedList class shown above 
    def insertAfter(self, prev_node, new_data):

        # 1. Check if the given prev_node exists
        if prev_node is None:
            print "The given previous node must inLinkedList."
            return

        #  2. Create new node &
        #     Put in the data
        new_node = Node(new_data)

        # 4. Make next of new Node as next 
        #    of prev_node
        new_node.next = prev_node.next

        # 5. make next of prev_node as new_node
        prev_node.next = new_node


    # This function is defined in Linked List class
    # Appends a new node at the end.  This method is
    # defined inside LinkedList class shown above */
    def append(self, new_data):

        # 1. Create a new node
        # 2. Put in the data
        # 3. Set next as None
        new_node = Node(new_data)

        # 4. If the Linked List is empty, then make the
        #    new node as head
        if self.head is None:
            self.head = new_node
            return

        # 5. Else traverse till the last node
        last = self.head
        while (last.next):
            last = last.next

        # 6. Change the next of last node
        last.next =  new_node

    # Utility function to print the 
    # linked list
    def printList(self):
        temp = self.head
        while (temp):
            print temp.data,
            temp = temp.next

# Code execution starts here
if __name__=='__main__':

    # Start with the empty list
    llist = LinkedList()

    # Insert 6.  So linked list 
    becomes 6->None
    llist.append(6)

    # Insert 7 at the beginning. So 
    # linked list becomes 7->6->None
    llist.push(7);

    # Insert 1 at the beginning. So 
    # linked list becomes 1->7->6->None
    llist.push(1);

    # Insert 4 at the end. So linked list 
    # becomes 1->7->6->4->None
    llist.append(4)

    # Insert 8, after 7. So linked list 
    # becomes 1 -> 7-> 8-> 6-> 4-> None
    llist.insertAfter(llist.head.next, 8)

    print 'Created linked list is:',
    llist.printList()
# This code is contributed by Manikantan Narasimhan