input: Write a function that creates a class named `ListNode` which is used to create nodes for a linked list in Python. The class should have an `__init__` method that initializes the `data` for the node and sets the `next` attribute to `None`.
  
  assert ListNode(10).data==10
  assert ListNode(10).next==None
output: class ListNode:
      def __init__(self, data):
          self.data = data
          self.next = None