Linked List OOP Implementation (without array)

linked_list_non_array.py

class ListNode:
    def __init__(self, DataValue):
        self._DataValue = DataValue
        self._NextNode = None
        
    def set_DataValue(self, DataValue):
        self._DataValue = DataValue

    def set_NextNode(self, NextNode):
        self._NextNode = NextNode

    def get_DataValue(self):
        return self._DataValue

    def get_NextNode(self):
        return self._NextNode

    def __str__(self):
        return str(self._DataValue)

class LinkedList:
    def __init__(self):
        self._Start = None

    def add(self, DataValue):

        def helper(CurNode, DataValue):

            if CurNode == None:
                new_node = ListNode(DataValue)
                return new_node

            elif CurNode.get_DataValue() < DataValue:
                CurNode.set_NextNode(helper(CurNode.get_NextNode(), DataValue))
                return CurNode

            else:
                new_node = ListNode(DataValue)
                new_node.set_NextNode(CurNode)
                return new_node

        self._Start = helper(self._Start, DataValue)

    def delete(self, DataValue):

        def helper(CurNode, DataValue):

            if CurNode == None:
                return None # not found

            elif CurNode.get_DataValue() == DataValue:
                return CurNode.get_NextNode()

            else:
                CurNode.set_NextNode(helper(CurNode.get_NextNode(), DataValue))
                return CurNode

        self._Start = helper(self._Start, DataValue)

    def search(self, DataValue):

        def helper(CurNode, DataValue):

            if CurNode == None:
                return False

            elif CurNode.get_DataValue() == DataValue:
                return True

            else:
                return helper(CurNode.get_NextNode(), DataValue)

        return helper(self._Start, DataValue)

    def display(self):

        print('Linked List: ', end = '')
        CurNode = self._Start
        while CurNode:
            print(CurNode, end = ' ')
            CurNode = CurNode.get_NextNode()
        print()

    def size(self):

        count = 0
        CurNode = self._Start
        while CurNode:
            count += 1
            CurNode = CurNode.get_NextNode()

        return count