在 __init__() 方法中设置 class 实例的 python 是什么？

Question

I'd like to send in a list of dependencies as part of creating a DAGNode : what is the supported way to achieve a similar behavior in python - given it seems this exact syntax were not supported?

from typing import TypeVar, Generic

T = TypeVar('T')
class DAGNode(Generic[T]):

    # Apparently the `DAGNode` type does not exist yet so this fails
    def __init__(self, id: T, dependencies: set[DAGNode[T]]):  
        self.id = id
        self.dependencies = dependencies

Answer 1

Since the class does not exist yet you have to reference it including its name between single quote like this

from typing import TypeVar, Generic, Set

T = TypeVar('T')
class DAGNode(Generic[T]):

    # Apparently the DAGNode type does not exist yet so this fails
    def __init__(self, type_id: T, dependencies: Set['DAGNode[T]']):  
        self.id = type_id
        self.dependencies = dependencies

Notice I used type_id instead of id to not shadow the builtin function id

Answer 2

In Python 3.7 and later, you can add the line

from __future__ import annotations

near the beginning of the code. Annotations aren't evaluated then anymore automatically (only valid expression syntax is checked).

For more details see https://peps.python.org/pep-0563/