old_contents: """An implementation of a doubly linked list in Python."""
  
  
  class Node():
      """Instantiate a node."""
  
      def __init__(self, value=None, nxt=None, previous=None):
          self.value = value
          self.next = nxt
          self.previous = previous
  
  
  class DbLinkedList():
      """Instantiate a doubly linked list."""
  
      def __init__(self, value=None):
          self.head = None
          self.tail = None
          if value:
              self.push(value)
  
      def push(self, value=None):
          """Pushes vale to the head of dll."""
          new_node = Node(value, self.head, None)
          orig_node = self.head
          self.head = new_node
          new_node.next = orig_node
          new_node.prev_node = None
          if self.tail is None:
              self.tail = orig_node
  
  
new_contents: """An implementation of a doubly linked list in Python."""
  
  
  class Node():
      """Instantiate a node."""
  
      def __init__(self, value=None, nxt=None, previous=None):
          """."""
          self.value = value
          self.next = nxt
          self.previous = previous
  
  
  class DbLinkedList():
      """Instantiate a doubly linked list."""
  
      def __init__(self, value=None):
          """."""
          self.head = None
          self.tail = None
          if value:
              self.push(value)
  
      def push(self, value=None):
          """Push value to the head of dll."""
          new_node = Node(value, self.head, None)
          orig_node = self.head
          self.head = new_node
          new_node.next = orig_node
          if self.tail is None:
              self.tail = self.head
  
      def append(self, value):
          """Append value to the tail of dll."""
          new_node = Node(value, None, self.tail)
          orig_node = self.tail
          self.tail = new_node
          new_node.prev_node = orig_node
          if self.head is None:
              self.head = self.tail
  
      def pop(self):
          """Pop first value off of the head of dll."""
  
subject: append method written. switching drivers for test.