old_contents: #!/usr/bin/env python
  # -*- coding:utf-8 -*-
  from __future__ import division
  from __future__ import unicode_literals
  from __future__ import print_function
  
  
  class Node(object):
      def __init__(self, data, next):
          self.data = data
          self.next = next
  
  
  class LinkedList(object):
      def __init__(self):
          self.head = None
  
new_contents: #!/usr/bin/env python
  # -*- coding:utf-8 -*-
  from __future__ import division
  from __future__ import unicode_literals
  from __future__ import print_function
  
  
  class Node(object):
      def __init__(self, data, next=None):
          self.data = data
          self.next = next
          self.size = 0
  
  
  class LinkedList(object):
      def __init__(self):
          self.head = None
  
      def __len__(self):
          return self.size
  
      def insert(self, data):
          self.head = Node(data, self.head)
          self.size += 1
  
      def append(self, data):
          temp = self.head
          while temp.next:
              temp = temp.next
          temp.next = Node(data)
          self.size += 1
  
subject: add basic implementation of linked list