Descriptor with meta class vs traditional

Question

I’ve been watching the videos (example) by Luciano Ramalho on Descriptors with metaclass.

I wanted to know the advantage of this model in relation to the more traditional implementation of Descriptors as that example in the documentation:

class RevealAccess(object):
    """A data descriptor that sets and returns values
       normally and prints a message logging their access.
    """

    def __init__(self, initval=None, name='var'):
        self.val = initval
        self.name = name

    def __get__(self, obj, objtype):
        print('Retrieving', self.name)
        return self.val

    def __set__(self, obj, val):
        print('Updating', self.name)
        self.val = val

>>> class MyClass(object):
...     x = RevealAccess(10, 'var "x"')
...     y = 5
...
>>> m = MyClass()
>>> m.x
Retrieving var "x"
10
>>> m.x = 20
Updating var "x"
>>> m.x
Retrieving var "x"
20
>>> m.y
5

---

I made a test and to me it seemed to work equal. I also noticed that in the example of documentation the methods getattr and setattr are not used as in example luciano:

class Quantidade(object):
    def __init__(self)
        self.set_nome(self.__class__.__name__, id(self))

    def set_nome(self, prefix, key):
        self.nome_alvo = '%s_%s' % (prefix, key)

    def __get__(self, instance, owner):
        return getattr(instance, self.nome_alvo)

    def __set__(self, instance, value):
        if value > 0:
            setattr(instance, self.nome_alvo, value)
        else:
            raise ValueError('valor deve ser > 0')


class ModeloMeta(type):
    def __init__(cls, nome, bases, dic):
        super(ModeloMeta, cls).__init__(nome, bases, dic)
        for chave, attr in dic.items():
            if hasattr(atr, 'set_nome'):
                attr.set_nome('__' + nome, chave)

class Modelo(object):
    __metaclass__ = ModeloMeta


class ItemPedido(Modelo):
    peso = Quantidade()
    preco = Quantidade()

    def __init__(self, descricao, peso, preco):
        self.descricao = descricao
        self.peso = peso
        self.preco = preco

Answer 1

In fact I was completely outdated with regard to the new features of python3.6+. Python3.6 introduced the descriptor protocol object.__set_name__(self, owner, name) called at the time the class is created. Therefore, I think it is no longer necessary to use metaclass to work with Descriptors from Python3.6+. Follows publishing I used to read about the theme, it even makes comparisons between the new version and the legacy mode.