import math

class PositiveNumber:

def __set_name__(self, owner, name):

self._name = name

def __get__(self, instance, owner):

return instance.__dict__[self._name]

def __set__(self, instance, value):

if (not isinstance(value, int | float)) or value <= 0:

raise ValueError("positive number expected")

instance.__dict__[self._name] = value

class Circle:

radius = PositiveNumber()

def __init__(self, radius):

self.radius = radius

def area(self):

return round(math.pi * self.radius**2, 2)

class Square:

side = PositiveNumber()

def __init__(self, side):

self.side = side

def area(self):

return round(self.side**2, 2)