mypy circular import problem

circular_import_solution.py

# circular import:

# node.py

from typing import Iterable
from nodeset import NodeSet

from typing import Iterable

from abstract_node import AbstractNode
from nodeset import NodeSet


class Node:
    def __init__(self, name):
        self.name = name
        self.children = NodeSet()

    def do_stuff(self) -> None:
        print(f'node {self.name} does stuff')

    def descendants(self) -> Iterable['Node']:
        for child in self.children.all_nodes():
            yield child
            yield from child.descendants()

# nodeset.py
from typing import Iterable, List

from node import Node

class NodeSet:

    def __init__(self):
        self.nodes: List[Node] = []

    def insert(self, node: Node) -> None:
        self.nodes.append(node)

    def all_nodes(self) -> Iterable[Node]:
        for node in self.nodes:
            yield node


# app.py



from node import Node


n = Node('a')

n.children.insert(Node('b'))
n.children.insert(Node('c'))
n.children.insert(Node('d'))

root = Node('r')
root.children.insert(n)


for d in root.descendants():
    d.do_stuff()


# если запустить это:
Traceback (most recent call last):
  File "/Users/1111/_projects/fasttrack/constructor/run_nodes.py", line 3, in <module>
    from node import Node
  File "/Users/1111/_projects/fasttrack/constructor/node.py", line 4, in <module>
    from nodeset import NodeSet
  File "/Users/1111/_projects/fasttrack/constructor/nodeset.py", line 3, in <module>
    from node import Node
ImportError: cannot import name 'Node'

  
# ===========================================
# Решение проблемы: наследуем ноду от AbstractNode.
# NodeSet не обязан знать, что у него в списке лежат именно ноды. Пусть знает только об AbstractNode



# abstract_node.py

from abc import ABC, abstractmethod
from typing import Iterable

class AbstractNode(ABC):

    @abstractmethod
    def descendants(self) -> Iterable['AbstractNode']:
        pass
      
    @abstractmethod
    def do_stuff(self) -> None:
        pass


# node_set.py

# NodeSet не обязан знать, что у него в списке хранятся именно ноды. Это всего лишь коллекция. 
# пусть знает только об интерфейсе
from typing import Iterable, List

from abstract_node import AbstractNode

class NodeSet:

    def __init__(self):
        self.nodes: List[AbstractNode] = []

    def insert(self, node: AbstractNode) -> None:
        self.nodes.append(node)

    def all_nodes(self) -> Iterable[AbstractNode]:
        for node in self.nodes:
            yield node

    def all_descendants(self) -> Iterable[AbstractNode]:
        for node in self.nodes:
            yield node
            yield from node.descendants()


# node.py
from typing import Iterable

from abstract_node import AbstractNode
from nodeset import NodeSet


class Node(AbstractNode):
    def __init__(self, name):
        self.name = name
        self.children = NodeSet()

    def do_stuff(self) -> None:
        print(f'node {self.name} does stuff')

    def descendants(self) -> Iterable['AbstractNode']:
        yield from self.children.all_descendants()