如何让代码块在变量更改时运行？

class Observable:
    def __init__(self):
        self.observers = []

    def add_observer(self, observer):
        self.observers.append(observer)

    def remove_observer(self, observer):
        self.observers.remove(observer)

    def notify_observers(self):
        for observer in self.observers:
            observer.update()

class Variable(Observable):
    def __init__(self):
        super().__init__()
        self.value = None

    def set_value(self, value):
        self.value = value
        self.notify_observers()

class Observer:
    def __init__(self, variable):
        self.variable = variable

    def update(self):
        # 在变量更改时执行的代码块
        print("Variable changed:", self.variable.value)

# 创建一个变量对象
variable = Variable()

# 创建观察者对象
observer = Observer(variable)

# 将观察者对象添加到变量对象的观察者列表中
variable.add_observer(observer)

# 设置变量的值，触发代码块的执行
variable.set_value(10)