import collections
from typing import Iterable
from unittest import TestCase


class Node(collections.UserList):
    owner: None = None


class Leaf(Node):
    pass


class Tree(Node):
    def __init__(self, seq: Iterable[Node] = None):
        if seq is None:
            seq = []
        for node in seq:
            node.owner = self
        super(Tree, self).__init__(seq)

    def __setitem__(self, key, value):
        if type(key) is int:
            self[key].pred = None
            value.pred = self
        else:  # slice
            for old, new in zip(self[key], value):
                old.owner = None
                new.owner = self
        return super(Tree, self).__setitem__(key, value)


class TestTree(TestCase):
    def test___setitem__(self):
        ls = [Leaf([n]) for n in range(6)]  # ls = [[0], [1], [2], ..., [5]]
        d = Tree(ls[:4])  # d = [[0], [1], [2], [3]]
        d[0:2] = ls[4:6]  # d = [[4], [5], [2], [3]]
        self.assertListEqual([d, d], [ls[4].owner, ls[5].owner])  # pass
        print(d[0].owner)  # [[4], [5], [2], [3]]
        _ = d[0:1]
        print(d[0].owner)  # [[4]] ???

        print(d[1].owner)  # [[4], [5], [2], [3]]
        _ = d[0:2]
        print(d[0].owner)  # [[4], [5]] ???
        print(d[1].owner)  # [[4], [5]] ???

        print(d[0].owner == d[0:1])  # False
        self.assertEqual(d[0:1], d[0].owner)  # pass ???
        self.assertEqual(d[0:2], d[0].owner)  # pass ???