Objects/descrobject.c (part 9)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/descrobject.c ↗

This annotation covers class-level descriptors. See objects_descrobject8_detail for slot_wrapper, method-wrapper, property, and classmethod_descriptor.

Map

Lines	Symbol	Role
1-80	classmethod.__get__	Bind class method to class
81-160	staticmethod.__get__	Return wrapped function unchanged
161-240	member_descriptor.__get__	Read a C struct member via offset
241-320	getset_descriptor.__get__	Call a C getter function
321-600	PyMemberDef / PyGetSetDef	C-level field definition structures

Reading

classmethod.__get__

// CPython: Objects/descrobject.c:640 cm_descr_get
static PyObject *
cm_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
    classmethod *cm = (classmethod *)self;
    if (type == NULL) {
        if (obj != NULL)
            type = (PyObject *)(Py_TYPE(obj));
        else {
            PyErr_SetString(PyExc_TypeError, "descriptor 'classmethod' needs a type");
            return NULL;
        }
    }
    if (Py_TYPE(cm->cm_callable)->tp_descr_get != NULL) {
        return Py_TYPE(cm->cm_callable)->tp_descr_get(
            cm->cm_callable, type, (PyObject *)(Py_TYPE(type)));
    }
    return PyMethod_New(cm->cm_callable, type);
}

classmethod.__get__ binds the wrapped function to the class (not the instance). @classmethod def foo(cls): cls is the class on which the method is called, which may be a subclass. type parameter can be None if accessed from an instance.

staticmethod.__get__

// CPython: Objects/descrobject.c:700 sm_descr_get
static PyObject *
sm_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
    staticmethod *sm = (staticmethod *)self;
    if (sm->sm_callable == NULL) {
        PyErr_SetString(PyExc_RuntimeError, "uninitialized staticmethod object");
        return NULL;
    }
    if (Py_TYPE(sm->sm_callable)->tp_descr_get != NULL) {
        return Py_TYPE(sm->sm_callable)->tp_descr_get(
            sm->sm_callable, NULL, type);
    }
    return Py_NewRef(sm->sm_callable);
}

staticmethod.__get__ simply returns the wrapped callable unchanged. No binding occurs; obj and type are ignored. @staticmethod is purely a descriptor that prevents the normal method binding.

member_descriptor

// CPython: Objects/descrobject.c:80 member_get
static PyObject *
member_get(PyMemberDescrObject *descr, PyObject *obj, PyObject *type)
{
    if (descr_check((PyDescrObject *)descr, obj, &res) < 0) return NULL;
    return PyMember_GetOne((char *)obj, descr->d_member);
}

PyObject *
PyMember_GetOne(const char *addr, PyMemberDef *l)
{
    addr += l->offset;
    switch (l->type) {
    case T_INT:    return PyLong_FromLong(*(int*)addr);
    case T_FLOAT:  return PyFloat_FromDouble(*(float*)addr);
    case T_STRING: return PyUnicode_FromString(*(char**)addr);
    ...
    }
}

member_descriptor reads C struct fields by offset. Used for type attributes like int.real, complex.real, complex.imag, and many others that map directly to C struct members.

gopy notes

classmethod.__get__ is objects.ClassMethodGet in objects/descr.go. It returns a objects.BoundMethod binding the method to the class. staticmethod.__get__ returns the callable unchanged. member_descriptor reads Go struct fields via unsafe.Pointer arithmetic using the stored offset.