#
if __name__ == '__main__':
    a = SomeClass()
    b = SomeClass()
    print(id(a.myName))
    print(id(b.myName))
    print(a.myName)
    print(b.myName)
    a.myName = 'my name is A'
    print(a.myName)
    print(b.myName)
    b.myName = 'my name is B'
    print(a.myName)
    print(b.myName)
    del a.myName

 #
class SomeClass:
    myName = Name()  # вот эта вот...

  
class Nn: # дескриптор свойств nn
    """ счётчик обращений к name """
    def __get__(self, instance, owner):
        return owner._nn
    
    def __set__(self, instance, value):
        raise AttributeError('Нельзя изменить счётчик')
    
    def __delete__(self, instance):
        raise AttributeError('Нельзя удалить счётчик')
class Name: # дескриптор свойств name
    """ имя экземпляра """
    def __get__(self, instance, owner):
        owner._nn += 1
        return '[%d] %s' % (owner._nn, instance._name)
    
    def __set__(self, instance, value):
        instance._name = value
    def __delete__(self, instance):
        raise AttributeError('Нельзя удалить имя экземпляра')
class D: # класс-клиент
    def __init__(self):
        D._nn = 0
        self._name = 'по-умолчанию'
    nn = Nn()
    name = Name()
#---------------------------------------------------------------------------------
if __name__ == '__main__':
    a, b, c = D(), D(), D()
    a.name = 'my name is A'
    b.name = 'my name is B'
    c.name = 'my name is C'
    print(a.name)
    print(b.name)
    print(c.name)
    print(a.nn)
    print(b.nn)
    print(c.nn)

 ================= RESTART: D:\web.py\attrs\mydescriptors.py =================
[1] my name is A
[2] my name is B
[3] my name is C
3
3
3
>>>

 class D: # класс-клиент
    def __init__(self):
        D._nn = 0
        self._name = 'по-умолчанию'
    nn = Nn()
    name = Name()  #  вот эта ...