input: Write a function to implement a linked list in Python using classes. The function should include classes for the nodes and the linked list, and should provide a method to print the linked list. The function should also include an example of how to create and link nodes in the linked list, and print it out.
  assert LinkedList().print_list() == None
  assert node1.data == 1
  assert node2.next == node3
output: class Node:
      def __init__(self, data):
          self.data = data
          self.next = None
  
  class LinkedList:
      def __init__(self):
          self.head = None
  
      def print_list(self):
          current = self.head
          while current:
              print(current.data, end=" ")
              current = current.next