input: Write a function that defines a class to create a linked list in Python nodes. The class should be named `ListNode` and have an `__init__` method to initialize the node with data and set the next node to `None`.
  
  assert ListNode(5).data==5
  assert ListNode(5).next==None
  assert ListNode(10).data==10
  assert ListNode(10).next==None
output: class ListNode:
      def __init__(self, data):
          self.data = data
          self.next = None