Cython中实现SlotsMeta元类遇问题，求解决方案

我想在Cython里实现一个名为SlotsMeta的元类，目标是让使用这个元类的类，其所有类变量都变成Cython中的readonly属性。我的思路是把元类__cinit__方法传入的**kwargs里的类变量（作为键）转成Tuple[str]，再赋值给SlotsMeta.__slots__。

参考了以下资料：

• Python Metaclass defining slots makes slots readonly
• sagelib的classcall_metaclass.pxd实现
• sagelib的classcall_metaclass.pyx实现

我的Cython实现代码如下：

#cython: language_level=3
# copied from sagelib的classcall_metaclass.pyx
from cpython cimport PyObject, Py_XDECREF

cdef extern from "Python.h":
    ctypedef PyObject *(*callfunc)(type, object, object) except NULL
    ctypedef struct PyTypeObject_call "PyTypeObject":
        callfunc tp_call # needed to call type.__call__ at very high speed.
    cdef PyTypeObject_call PyType_Type # Python's type

cdef class SlotsMeta(type):
    cdef readonly tuple __slots__

    def __init__(mcls, str name, tuple bases, dict attrs):
        attrs_keys = tuple(str(k) for k in attrs.keys())
        mcls.__slots__ = attrs_keys

    def __call__(cls, *args, **kwargs):
        ptr = PyType_Type.tp_call(cls, args, kwargs)
        inst = <object>ptr
        inst.__init__(*args, **kwargs)
        Py_XDECREF(ptr) # During the cast to <object> Cython did INCREF(res)
        return inst

测试代码执行失败：

class A(metaclass=SlotsMeta):
    B: str = "H"
 
    
def test_slotsmeta():
    a = A() # passes
    assert a.B == "H" # passes
    with pytest.raises(AttributeError): # passes
        a.C # passes
    with pytest.raises(AttributeError):
        a.C = 500 # failed
        
    assert a.__slots__ == ("B", ) # failed

目前遇到的问题：

• 本应无法给实例a添加属性C（a.C = 500），但实际可以执行成功
• a.__slots__应该返回("B",)，但实际没有返回预期值
• 实例a的__dict__本不应存在，但实际存在

内容的提问来源于stack exchange，提问作者Jim