Python: circular imports needed for type checking

Question

First of all: I do know that there are already many questions and answers to the topic of the circular imports.

The answer is more or less: \"Design your Module/Class s

Answer 1

Possible duplicate: Python type hinting without cyclic imports

You should use Forward Reference (PEP 484 - Type Hints):

When a type hint contains names that have not been defined yet, that definition may be expressed as a string literal, to be resolved later.

So instead of:

class Tree:
def __init__(self, left: Tree, right: Tree):
    self.left = left
    self.right = right

do:

class Tree:
def __init__(self, left: 'Tree', right: 'Tree'):
    self.left = left
    self.right = right