many-to-many relation through association select statement

from sqlalchemy import Integer, String, Column, create_engine, or_, select
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import (relationship, sessionmaker, aliased, join, foreign,
                            remote)

engine = create_engine('sqlite:///:memory:', echo=True)
Base = declarative_base()

_next_two_nodes = None
def next_two_nodes_select():
    global _next_two_nodes
    if _next_two_nodes is None:
        _leftside = aliased(Node, name="leftside")
        _rightside = aliased(Node, name="rightside")
        _next_two_nodes = select(
            [_leftside.id.label("left_node_id"),
             _rightside.id.label("right_node_id")]
        ).select_from(
            join(
                _leftside, _rightside,
                or_(
                    _leftside.id + 1 == _rightside.id,
                    _leftside.id + 2 == _rightside.id
                )
            )
        ).alias()
    return _next_two_nodes


class Node(Base):
    __tablename__ = 'node'
    id = Column(Integer, primary_key=True)
    label = Column(String, unique=True)
    next_two_nodes = relationship(
        "Node", secondary=next_two_nodes_select,
        primaryjoin=(lambda: foreign(Node.id)
                     == remote(next_two_nodes_select().c.left_node_id)),
        secondaryjoin=(lambda: foreign(next_two_nodes_select().c.right_node_id)
                       == remote(Node.id)),
        backref="previous_two_nodes",
        viewonly=True
    )

    def __repr__(self):
        return "Node(id={}, Label={})".format(self.id, self.label)


Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()

nodes = [
    Node(id=1, label="Node1"),
    Node(id=2, label="Node2"),
    Node(id=3, label="Node3"),
    Node(id=4, label="Node4")
]
session.add_all(nodes)
session.commit()

node = session.query(Node).filter_by(id=2).one()
print(node.next_two_nodes)
print(node.previous_two_nodes)

NodeAlias = aliased(Node)
print(session.query(Node).join(NodeAlias, Node.next_two_nodes).filter(NodeAlias.id == 3).all())