input: Write a function to implement a linked list using classes in Python. The function should include classes for the node and the linked list, and methods to print the linked list. If the linked list is empty, it should print nothing.
  assert linked_list_implementation().print_list() == None
  assert linked_list_implementation().insert(1).insert(2).insert(3).print_list() == "1\n2\n3\n"
  assert linked_list_implementation().insert(4).insert(5).insert(1).print_list() == "4\n5\n1\n"
  assert linked_list_implementation().insert(3).insert(1).insert(2).print_list() == "3\n1\n2\n"
output: class Node:
      def __init__(self, data):
          self.data = data
          self.next = None
  
  class LinkedList:
      def __init__(self):
          self.head = None
  
      def insert(self, data):
          new_node = Node(data)
          if self.head is None:
              self.head = new_node
          else:
              current = self.head
              while current.next:
                  current = current.next
              current.next = new_node
          return self
  
      def print_list(self):
          current = self.head
          while current:
              print(current.data)
              current = current.next