Property Descriptors

@property

class Rectangle:
    def __init__(self, width: float, height: float):
        self._width = width
        self._height = height

    @property
    def area(self) -> float:
        return self._width * self._height

    @property
    def perimeter(self) -> float:
        return 2 * (self._width + self._height)

@cached_property

from functools import cached_property

class DataSet:
    def __init__(self, raw: list[float]):
        self.raw = raw

    @cached_property
    def mean(self) -> float:
        return sum(self.raw) / len(self.raw)

    @cached_property
    def variance(self) -> float:
        m = self.mean
        return sum((x - m) ** 2 for x in self.raw) / len(self.raw)