I was just starting to learn @property to implement getter and setter method in Python. I know that for it not to end up as a RecursionError, we have to change the attribute name locally, like putting an underscore as a prefix. But when I try to implement it, I got an AttributeError that says the object (a subclass) missing the particular attribute that I changed, as I mentioned earlier, in its superclass. Here is my code.

class Handler(ABC):
    @property
    def parent(self) -> Handler:
        return self._parent
    
    @parent.setter
    def parent(self, parent: Handler):
        self._parent = parent

    @abstractmethod
    def handle(self):
        pass

    def add_child(self, child):
        pass

class ThingHandler(Handler):
    def __init__(self, name):
        self.name = name
        self.string = self._make_string()
        self._children: List[Handler] = list()

    def handle(self):
        ... # method implementation, not important atm.
    
    def add_child(self, child: Handler):
        self._children.append(child)
        child.parent = self

    def __str__(self):
        return self.string

    def _make_string(self):
        name = self.name.lower().replace(" ", "_")
        return str(self.parent) + f".{name}"

I was just trying to initialize the ThingHandler when I got an error in the _make_string method specifically in the last line where I call self.parent. The error message is

AttributeError: 'ThingHandler' object has no attribute '_parent'. Did you mean: 'parent'?

referring to the return self._parent line in Handler. I was also experimenting with python’s ABC in case it has something to do with the error.

Any solution/suggestion?