在python中,槽描述符是如何工作的?
我知道插槽的功能和它的用途 然而,对于使用在python中,槽描述符是如何工作的?,python,immutability,metaclass,slots,python-descriptors,Python,Immutability,Metaclass,Slots,Python Descriptors,我知道插槽的功能和它的用途 然而,对于使用\uuuuu插槽创建的成员描述符的底层机制如何工作,我还没有找到一个全面的答案 对象级别的值实际存储在哪里 有没有办法在不直接访问描述符的情况下更改这些值? (例如,当类C具有\uuuuu dict\uuuuu时,您可以执行C.\uuuu dict\uuuu['key']而不是C.key) 通过创建类似的类级描述符,可以“扩展”定义\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
\uuuuu插槽
创建的成员
描述符的底层机制如何工作,我还没有找到一个全面的答案
对象级别的值实际存储在哪里
有没有办法在不直接访问描述符的情况下更改这些值?(例如,当类
C
具有\uuuuu dict\uuuuu
时,您可以执行C.\uuuu dict\uuuu['key']
而不是C.key
)
通过创建类似的类级描述符,可以“扩展”定义
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu?并作进一步阐述,;是否可以使用元类构建一个不可变的对象,但不通过手动创建所述描述符来明确定义\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
,\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu,与访问的类相关联的描述符实际上使用CPython中的本机C方法来设置和检索作为C结构的类实例上每个slot属性的Python对象的引用
用Python表示的插槽描述符,名称为member\u descriptor
,定义如下:
如果不使用CTypes与本机代码交互,就无法从纯Python代码中执行或增强这些描述符
有可能通过以下方式达到他们的类型
class A:
__slots__ = "a"
member_descriptor = type(A.a)
然后我们可以假设可以从它继承,并编写派生的\uuuuu get\uuuu
和\uuuu set\uuuuu
方法,这些方法可以进行检查等等,但不幸的是,它不能作为基类工作
但是,可以编写其他并行描述符,这些描述符可以调用本机描述符来实际存储值。
通过使用元类,可以在类创建时重命名传入的\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
并将它们的访问权封装在自定义描述符中
因此,对于一个简单的类型检查变量元类,可以
class TypedSlot:
def __init__(self, name, type_):
self.name = name
self.type = type_
def __get__(self, instance, owner):
if not instance:
return self
return getattr(instance, "_" + self.name)
def __set__(self, instance, value):
if not isinstance(value, self.type):
raise TypeError
setattr(instance, "_" + self.name, value)
class M(type):
def __new__(metacls, name, bases, namespace):
new_slots = []
for key, type_ in namespace.get("__slots__", {}).items():
namespace[key] = TypedSlot(key, type_)
new_slots.append("_" + key)
namespace["__slots__"] = new_slots
return super().__new__(metacls, name, bases, namespace)
def __dir__(cls):
return [name for name in super().__dir__() if name not in cls.__slots__]