old_contents: #!/usr/bin/env python
  from __future__ import unicode_literals
  
  
  class Node(object):
      ''' Create data Node with default value and next pointer. '''
      def __init__(self, value, ahead=None, behind=None):
          ''' Value and next pointer default to none. '''
          self.val = value
          self.ahead = ahead
          self.behind = behind
  
  
  class DLL(object):
      ''' Create an empty DLL. '''
      def __init__(self):
          self.head = None
          self.tail = None
  
      def insert(self, value):
          ''' Add data Node to the tail of DLL. '''
          self.tail = Node(value, self.tail)
  
          if not self.head:
              self.head = self.tail
          else:
              self.tail.ahead.behind = self.tail
  
      def pop():
          ''' Remove head Node from head of DLL. Reassign head data
              Node and return value of deDLLd Node. '''
          try:
              val = self.head.val
          except AttributeError:
              ''' Mimic error message from list '''
              raise IndexError("deDLL from empty Stack")
          self.head.behind.ahead, self.head = None, self.head.behind
          return val
  
      def append(self, value):
          ''' Add data Node to the tail of DLL. '''
          self.tail = Node(value, self.tail)
  
          if not self.head:
              self.head = self.tail
          else:
              self.tail.ahead.behind = self.tail
  
      def shift():
          ''' Remove head Node from head of DLL. Reassign head data
              Node and return value of deDLLd Node. '''
          try:
              val = self.head.val
          except AttributeError:
              ''' Mimic error message from list '''
              raise IndexError("deDLL from empty Stack")
          self.head.behind.ahead, self.head = None, self.head.behind
          return val
  
      def size(self):
          ''' Return size of DLL (number of Nodes). '''
          count = 0
          current = self.tail
          while current:
              count += 1
              current = current.ahead
          return count
  
new_contents: #!/usr/bin/env python
  from __future__ import unicode_literals
  
  
  class Node(object):
      ''' Create data Node with default value and next pointer. '''
      def __init__(self, value, ahead=None, behind=None):
          ''' Value and next pointer default to none. '''
          self.val = value
          self.ahead = ahead
          self.behind = behind
  
  
  class DLL(object):
      ''' Create an empty DLL. '''
      def __init__(self):
          self.head = None
          self.tail = None
  
      def insert(self, value):
          ''' Add data Node to the tail of DLL. '''
          self.tail = Node(value, self.tail)
  
          if not self.head:
              self.head = self.tail
          else:
              self.tail.ahead.behind = self.tail
  
      def pop():
          ''' Remove head Node from head of DLL. Reassign head data
              Node and return value of deDLLd Node. '''
          try:
              val = self.head.val
          except AttributeError:
              ''' Mimic error message from list '''
              raise IndexError("deDLL from empty Stack")
          self.head.behind.ahead, self.head = None, self.head.behind
          return val
  
      def append(self, value):
          ''' Add data Node to the tail of DLL. '''
          self.tail = Node(value, self.tail)
  
          if not self.head:
              self.head = self.tail
          else:
              self.tail.ahead.behind = self.tail
  
      def shift():
          ''' Remove head Node from head of DLL. Reassign head data
              Node and return value of deDLLd Node. '''
          try:
              val = self.head.val
          except AttributeError:
              ''' Mimic error message from list '''
              raise IndexError("deDLL from empty Stack")
          self.head.behind.ahead, self.head = None, self.head.behind
          return val
  
      def remove(self):
          ''' Return size of DLL (number of Nodes). '''
          count = 0
          current = self.tail
          while current:
              count += 1
              current = current.ahead
          return count
  
subject: rename functions.