SINGLE LINKED LIST INSERTION AND DELETION.py

# A single node of a singly linked list
class Node:
  # constructor
  def __init__(self, data = None, next=None): 
    self.data = data
    self.next = next

# A Linked List class with a single head node
class LinkedList:
  def __init__(self):  
    self.head = None

  #############################################
  ############ INSERT NODES ###################
  #############################################

  ######### AT THE END (APPEND) ###############
  def append(self, data):
    newNode = Node(data)  ## Taking the data in the as a newNode
    if(self.head):        ## if self.head is not None then     means :=>> Linked list is not empty 
      current = self.head ## define current node as head node
      while(current.next):## While current node is not None
        current = current.next# increase the current node by one node
      current.next = newNode ## current node next is equal to newNode
    else:
      self.head = newNode  ## linked list is empty then simply add the new node
  
  ######### AT THE START (PREPAND) #############
  def prepand(self,data):
      newNode = Node(data) ## Create a node
      newNode.next = self.head ## Ponit the next of the new node to the head
      self.head = newNode ## paas the head to the new node
  
  ######### AFTER A NODE  #######################
  def add(self,prev_node,data):
      if not prev_node:
          print("Previous node is not in the list")
          return
      else:
          newNode = Node(data)
          newNode.next = prev_node.next
          prev_node.next = newNode
  
  ######### PRINTING ALL THE ELEMENTS  ##############
  def printLL(self):
    current = self.head   ## current node as head 
    while(current):       ## While current node is  not None
      print(current.data) ## Print the data part of the node   |data|next|
      current = current.next ## Increase the current node with one node

  ##################################################
  ############ DELETE NODES ########################
  ##################################################
  
  def delete_node(self,key):
    current = self.head

    ######### AT THE START ##########################
    if current and current.data == key:
      self.head = current.next
      current = None
      return 
    ######### IN THE MIDDLE AND THE END  ############
    prev = None
    while current and current.data != key:
      prev = current
      current = current.next
    if current is None:
      return
    else :
      prev.next = current.next
      current = None
    ##################################################
    ######## DELETE NODE AT A GIVEN POSITION   #######
    ##################################################    
  def delete_node_at_pos(self,pos):
    current = self.head

    if pos == 0:
      self.head = current.next
      current = None

    count = 1
    prev = None
    while current and count != pos:
      prev = current
      current = current.next
      count+=1
    if current is None:
      return
    else:
      prev.next = current.next
      current = None
    ##################################################
    ###### CALCULATE THE LENGTH OF THE LINKED LIST ### 
    ##################################################
  def length(self):
    current = self.head
    length = 0
    while(current):
      length+=1
      current = current.next
    return length


# Singly Linked List with insertion and print methods
LL = LinkedList()

LL.prepand("E")

LL.append("A")

LL.add(LL.head.next,"F")

LL.append("B")
LL.append("C")
LL.printLL()
print("\n")


LL.delete_node("B")
LL.printLL()
print("\n")
LL.delete_node_at_pos(0)
LL.printLL()
print("\n")
print(LL.length())