input: Write a function to implement a linked list using classes in Python. The function should include a Node class to represent the nodes and a LinkedList class to represent the entire linked list. The LinkedList class should also have a method to print the list.
  assert LinkedList().print_list() == None
  assert LinkedList().head == None
  linked_list = LinkedList()
  node1 = Node(1)
  node2 = Node(2)
  node3 = Node(3)
  linked_list.head = node1
  node1.next = node2
  node2.next = node3
  assert linked_list.print_list() == 1 2 3
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