Basic Python Linked List

linked_list.py

class Node:
    def __init__(self, val):
        self.__value = val
        self.__next = None

    def add(self, next_):
        self.__next = next_

    def value(self):
        return self.__value

    def next(self):
        return self.__next

    def size(self):
        size = 1
        next_ = self.next()
        while next_ is not None:
            size += 1
            next_ = next_.next()

        return size