Objects/descrobject.c (part 5)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/descrobject.c

This annotation covers slot-based descriptor dispatch and member descriptors. See objects_descrobject4_detail for PyWrapperDescrObject, slot_tp_call, slot_tp_repr, and slot_tp_hash.

Map

Lines	Symbol	Role
1-100	`slot_tp_descr_get`	Call `__get__` from a type's slot
101-200	`slot_tp_descr_set`	Call `__set__` / `__delete__` from a type's slot
201-340	`classmethod_get`	`classmethod.__get__` — bind to the class, not the instance
341-480	`staticmethod_get`	`staticmethod.__get__` — return the raw function
481-600	`member_get` / `member_set`	`PyMemberDef`-based descriptor for C struct fields
601-700	`PyMember_GetOne` / `PyMember_SetOne`	Read/write a C struct field by type code

Reading

`slot_tp_descr_get`

// CPython: Objects/descrobject.c:180 slot_tp_descr_get
static PyObject *
slot_tp_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
    /* Call self.__get__(obj, type) */
    PyObject *stack[2] = {obj, type};
    return vectorcall_maybe(tstate, &_Py_ID(__get__), self,
                            stack, 2 | PY_VECTORCALL_ARGUMENTS_OFFSET);
}

slot_tp_descr_get is installed as tp_descr_get when a class defines __get__. The descriptor protocol: obj.attr calls type(attr).__get__(attr, obj, type(obj)).

`classmethod_get`

// CPython: Objects/descrobject.c:220 cm_descr_get
static PyObject *
cm_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
    PyClassMethodObject *cm = (PyClassMethodObject *)self;
    if (type == NULL) {
        if (obj != NULL)
            type = (PyObject *)(Py_TYPE(obj));
        else {
            /* Neither obj nor type: return unbound */
            Py_INCREF(self);
            return self;
        }
    }
    /* Return a bound method: cm.func bound to type */
    return PyMethod_New(cm->cm_callable, type);
}

@classmethod installs cm_descr_get as tp_descr_get. Accessing MyClass.method or instance.method both return a bound method where the first argument is the class, not the instance.

`staticmethod_get`

// CPython: Objects/descrobject.c:300 sm_descr_get
static PyObject *
sm_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
    PyStaticMethodObject *sm = (PyStaticMethodObject *)self;
    /* Return the raw callable, not a bound method */
    Py_INCREF(sm->sm_callable);
    return sm->sm_callable;
}

@staticmethod simply returns the wrapped function regardless of how it is accessed. No self or cls is prepended.

`PyMember_GetOne`

// CPython: Objects/descrobject.c:620 PyMember_GetOne
PyObject *
PyMember_GetOne(const char *addr, PyMemberDef *l)
{
    /* Read a C struct field of the type described by l->type.
       Type codes: T_INT, T_DOUBLE, T_STRING, T_OBJECT, T_BOOL, etc. */
    switch (l->type) {
    case T_BOOL:
        return PyBool_FromLong(*(char *)(addr + l->offset));
    case T_INT:
        return PyLong_FromLong(*(int *)(addr + l->offset));
    case T_DOUBLE:
        return PyFloat_FromDouble(*(double *)(addr + l->offset));
    case T_OBJECT:
        v = *(PyObject **)(addr + l->offset);
        return Py_XNewRef(v);
    ...
    }
}

PyMemberDef descriptors give Python classes access to C struct fields. __slots__ is implemented using these member descriptors — each slot maps to a T_OBJECT field at a known offset in the instance struct.

gopy notes

slot_tp_descr_get is objects.SlotDescGet in objects/descr.go. classmethod_get is objects.ClassMethodGet. staticmethod_get is objects.StaticMethodGet. PyMember_GetOne/SetOne read from Go struct fields using unsafe.Pointer arithmetic in objects/member.go.

Map​

Reading​

slot_tp_descr_get​

classmethod_get​

staticmethod_get​

PyMember_GetOne​

gopy notes​

Map