如何在Python中阻止实例变量的外部修改？

class MyClass:
    def __init__(self):
        self._my_variable = 10

    @property
    def my_variable(self):
        return self._my_variable

    @my_variable.setter
    def my_variable(self, value):
        raise AttributeError("Cannot modify my_variable directly.")

obj = MyClass()
print(obj.my_variable)  # 输出：10
obj.my_variable = 20  # 抛出AttributeError异常

class MyClass:
    def __init__(self):
        self.__my_variable = 10

obj = MyClass()
print(obj.__my_variable)  # 抛出AttributeError异常
obj.__my_variable = 20  # 创建了一个新的实例变量，而不是修改原始的__my_variable
print(obj.__my_variable)  # 输出：20