class Vector: x = PositiveNumber(0) y = PositiveNumber(0) z = PositiveNumber(0) def __init__(self, x, y, z): self.x, self.y, self.z = x, y, z
class Thing: x = PositiveNumber()
class Thing: x = PositiveNumber(8) def __init__(self): self.x = -4
class Thing: x = PositiveNumber(4) y = PositiveNumber(5)