如何创建一个python字典只接受唯一可变对象

class UniqueDict(dict):
    def __setitem__(self, key, value):
        for k, v in self.items():
            if v is value:
                del self[k]
                break
        super().__setitem__(key, value)

my_dict = UniqueDict()
my_dict['key1'] = [1, 2, 3]
my_dict['key2'] = [4, 5, 6]
my_dict['key3'] = [1, 2, 3]  # 重复的值，会替换掉'key1'对应的值
my_dict['key4'] = [7, 8, 9]

print(my_dict)
# 输出：{'key2': [4, 5, 6], 'key3': [1, 2, 3], 'key4': [7, 8, 9]}