Python - NoneType object 在链接 getter 和 setter 时不可调用

Question

I'm trying to use @property and @propertyName.setter to get / set values on different properties but face the following issue when i chain multiple accessors.

This is a simple example i could reproduce my issue:

class Toto:

    def __init__(self):

        self._name = None
        self._label = None

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value


class Tata:

    def __init__(self):

        self._toto = Toto()

    @property
    def toto(self):
        return self._toto

    @toto.setter
    def toto(self, value):
        self._toto = value

When i execute this:

tata = Tata()
print("Toto name is", tata.toto.name)
tata.toto.name("titi")
print("Toto name is", tata.toto.name)

I obtain the following error:

Toto name is None
Traceback (most recent call last):
  File "/home/radjanidar/projects/music/demo/src/main/script/chainedproperties.py", line 43, in <module>
    tata.toto.name("titi")
TypeError: 'NoneType' object is not callable

Why can't i use the setter method on object Toto?

Answer 1

That's not how you use properties. Basically, properties are ways to make function calls act like attributes. When getting and setting them, the decorated getters and setters respectively are called, instead of performing naive attribute lookup.

Accordingly, you want tata.toto.name = 'titi' .

Answer 2

You've defined name as a property which changes how you interact with it.

Instead of tata.toto.name("titi") , you use tata.toto.name = "titi" .

https://docs.python.org/3/library/functions.html#property