input: Write a response that appropriately completes the request.
  
  Write a class to create a linked list in Python with nodes.
  
  class ListNode:
      def __init__(self, data):
          self.data = data
          self.next = None
output: class LinkedList:
      def __init__(self):
          self.head = None
  
      def append(self, data):
          new_node = ListNode(data)
          if not self.head:
              self.head = new_node
              return
          last_node = self.head
          while last_node.next:
              last_node = last_node.next
          last_node.next = new_node