Python描述符中的递归陷阱：内部属性命名策略解析

class ProblematicDescriptor:
    def __set_name__(self, owner, name):
        # 问题所在：内部存储名称与描述符的公开名称相同
        self.internal_name = name 

    def __get__(self, instance, owner):
        if instance is None:
            return self
        print(f"__get__ called for public name '{self.internal_name}'")
        # 此时，getattr(instance, 'some_attribute') 会再次触发描述符的 __get__ 方法
        # 因为 'some_attribute' 正是这个描述符在宿主类上的名称
        return getattr(instance, self.internal_name)

    def __set__(self, instance, value):
        if instance is None:
            return
        print(f"__set__ called for public name '{self.internal_name}'")
        # 同样，setattr(instance, 'some_attribute', value) 会再次触发描述符的 __set__ 方法
        setattr(instance, self.internal_name, value)

class HostClass:
    my_attr = ProblematicDescriptor()

# 尝试访问或设置属性将导致 RecursionError
# host_obj = HostClass()
# host_obj.my_attr = 10  # 尝试设置
# print(host_obj.my_attr) # 尝试获取

class SafeDescriptor:
    def __set_name__(self, owner, name):
        self.public_name = name
        # 解决方案：使用一个不同的内部存储名称，例如加上前缀 '_'
        self.internal_storage_name = f'_{name}' 

    def __get__(self, instance, owner):
        if instance is None:
            return self
        print(f"__get__ called for public name '{self.public_name}', retrieving from '{self.internal_storage_name}'")
        # 此时，getattr(instance, self.internal_storage_name) 会在实例的 __dict__ 中查找
        # 或者沿着 MRO 查找，而不会再次触发描述符协议，从而避免递归。
        return getattr(instance, self.internal_storage_name, None) # 提供默认值以防属性尚未设置

    def __set__(self, instance, value):
        if instance is None:
            return
        print(f"__set__ called for public name '{self.public_name}', storing to '{self.internal_storage_name}'")
        # setattr(instance, self.internal_storage_name, value) 将值存储为实例的一个普通属性
        setattr(instance, self.internal_storage_name, value)

class SafeHostClass:
    my_attr = SafeDescriptor()

# 示例：正确运行
safe_obj = SafeHostClass()
safe_obj.my_attr = 10
print(f"Retrieved value: {safe_obj.my_attr}")

# 验证实例的内部状态
print(f"Instance dictionary: {safe_obj.__dict__}") 
# 输出可能为: Instance dictionary: {'_my_attr': 10}