You can use Forward References as defined in PEP 484
A situation where this occurs commonly is the definition of a
container class, where the class being defined occurs in the signature
of some of the methods. For example, the following code (the start of
a simple binary tree implementation) does not work:
class Tree:
def __init__(self, left: Tree, right: Tree):
self.left = left
self.right = right
To address this, we write:
class Tree:
def __init__(self, left: 'Tree', right: 'Tree'):
self.left = left
self.right = right
It is allowable to use string literals as part of a type hint, for
example:
class Tree:
...
def leaves(self) -> List['Tree']:
