Python Double Linked List

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

  def __str__(self):
    return str(self.data)


class DLL:
  def __init__(self, head):
    self.head = head


  def addFront(self, data):
    new_node = Node(data)

    new_node.next = self.head
    if self.head:
      self.head.prev = new_node

    self.head = new_node


  def insertAfter(self, prev_node, new_data):
    if prev_node is None:
      raise Exception("prev_node must be specified!")

    new_node = Node(new_data)

    new_node.next = prev_node.next
    new_node.prev = prev_node

    if prev_node.next:
      prev_node.next.prev = new_node

    prev_node.next = new_node


  def append(self, data):
    new_node = Node(data)

    if not self.head:
      self.head = new_node
      return

    cur_node = self.head
    while cur_node.next:
      cur_node = cur_node.next

    cur_node.next = new_node
    new_node.prev = cur_node


  def insertBefore(self, next_node, data):
    new_node = Node(data)

    if next_node is None:
      raise Exception('next_node is not provided!')

    new_node.next = next_node
    new_node.prev = next_node.prev

    next_node.prev = new_node

    if new_node.prev:
      new_node.prev.next = new_node


  def __traverse(self, node):
    if node:
      print("{} === {} === {}".format(node.prev, node.data, node.next))
      self.__traverse(node.next)


  def traverse(self):
    self.__traverse(self.head)


n1 = Node(4)
dll = DLL(n1)
dll.addFront(3)
dll.addFront(56)
dll.addFront(32)

dll.insertAfter(n1, 23)
dll.insertAfter(n1, 22)

dll.traverse()