Python - Doubly Linked List Traversal

Traversing through a doubly linked list is very easy. It requires creating a temp node pointing to the head of the list. If the temp node is not null, display its content and move to the next node using temp next. Repeat the process till the temp node becomes null. If the temp node is empty at the start, then the list contains no item.

The function PrintList is created for this purpose. It is a 3-step process.

def PrintList(self):
  
  #1. create a temp node pointing to head
  temp = self.head
  
  #2. if the temp node is not null continue 
  #   displaying the content and move to the
  #   next node till the temp becomes null
  if(temp != None):
    print("The list contains:", end=" ")
    while (temp != None):
      print(temp.data, end=" ")
      temp = temp.next
    print()
  else:
    
    #3. If the temp node is null at the start, 
    #   the list is empty
    print("The list is empty.")

The below is a complete program that uses above discussed concept to traverse through the doubly linked list and displaying its content.

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None
    self.prev = None

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

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode
      newNode.prev = temp

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                  
MyList = LinkedList()

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)

#traverse to display the content of the list.
MyList.PrintList()

The above code will give the following output:

The list contains: 10 20 30