direct __slots__ attribute access in Cython

slot_access.pyx

from cpython cimport PyObject
from libc.string cimport strcmp

cdef extern from "Python.h":
    ctypedef struct PyTypeObject:
        pass

cdef extern from "structmember.h":
    ctypedef struct PyMemberDef:
        char *name
        int type
        Py_ssize_t offset
        int flags
        char *doc

cdef extern from "object.h":
    PyMemberDef *PyHeapType_GET_MEMBERS(PyTypeObject *type)
    Py_ssize_t Py_SIZE(obj)


def print_members(obj):
    t = type(obj)
    cdef Py_ssize_t n = Py_SIZE(t)
    cdef PyMemberDef *mp = PyHeapType_GET_MEMBERS(<PyTypeObject *> (<PyObject *> t))
    cdef Py_ssize_t i
    for i in range(n):
        print(mp[i].name)


def get_member_offset(obj, char *name):
    t = type(obj)
    cdef Py_ssize_t n = Py_SIZE(t)
    cdef PyMemberDef *mp = PyHeapType_GET_MEMBERS(<PyTypeObject *> (<PyObject *> t))
    cdef Py_ssize_t i
    for i in range(n):
        if strcmp(name, mp[i].name) == 0:
            return mp[i].offset


def get_value_at_offset(obj, Py_ssize_t offset):
    cdef PyObject *ret = (<PyObject **> (<char *>(<PyObject *>obj) + offset))[0]
    if ret == NULL:
        return None
    return <object> ret