import math
 
class Circulo():
 
    __slots__ = ("__raio")
 
    def __init__(self):
        super()
        self.__raio = None
 
    def get_perimetro(self):
        return 2 * math.pi * self.raio
 
    def get_area(self):
        return math.pi * self.raio ** 2
 
    @property
    def raio(self):
        return self.__raio
 
    @raio.setter
    def raio(self, x):
        self.__raio = x
 
c = Circulo()
c.raio = 2 # ok
c.lado = 2 # AttributeError

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