input: Write a function to create a class that defines a linked list node in Python. The class should have an initializer that takes in the data for the node and initializes the next pointer 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