Python类中的属性检查

class Person:
    def __init__(self, age):
        self._age = age

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        if value < 0:
            raise ValueError("Age cannot be negative.")
        self._age = value

person = Person(25)
print(person.age)  # 输出 25

person.age = 30
print(person.age)  # 输出 30

person.age = -5  # 抛出 ValueError 异常

def check_positive(func):
    def wrapper(instance, value):
        if value <= 0:
            raise ValueError("Value must be positive.")
        return func(instance, value)
    return wrapper

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

    @check_positive
    def width(self, value):
        self._width = value

    @check_positive
    def height(self, value):
        self._height = value

rect = Rectangle(10, 5)
print(rect.width)  # 输出 10

rect.width = 20
print(rect.width)  # 输出 20

rect.width = -5  # 抛出 ValueError 异常

class PositiveInteger:
    def __get__(self, instance, owner):
        return getattr(instance, '_value', None)

    def __set__(self, instance, value):
        if value <= 0:
            raise ValueError("Value must be positive.")
        setattr(instance, '_value', value)

class NumberHolder:
    value = PositiveInteger()

holder = NumberHolder()
print(holder.value)  # 输出 None

holder.value = 10
print(holder.value)  # 输出 10

holder.value = -5  # 抛出 ValueError 异常