Objects/descrobject.c (part 2)

cpython 3.14 @ ab2d84fe1023/Objects/descrobject.c ↗

This annotation covers property, classmethod, staticmethod, and mappingproxy in Objects/descrobject.c. For the core PyWrapperDescrObject and PyGetSetDescrObject see the objects_descr annotation.

Map

Lines	Symbol	Role
1-300	property object	getter/setter/deleter chaining, __get__/__set__/__delete__
301-600	classmethod_descriptor	Wraps a C function as a classmethod
601-800	staticmethod_descriptor	Wraps a C function as a static method
801-1100	slot_tp_descr_get	__get__ for slot wrappers
1101-1600	mappingproxy	Read-only proxy over a dict

Reading

property chaining

property(fget).setter(fset) creates a new property object copying the fget from the original and setting fset. This pattern allows @name.setter to add a setter to an existing property.

// CPython: Objects/descrobject.c:1380 property_setter
static PyObject *
property_setter(propertyobject *self, PyObject *args)
{
    return property_copy(self, NULL, PyTuple_GET_ITEM(args, 0), NULL);
}

classmethod_descriptor vs Python classmethod

classmethod_descriptor is the C-level equivalent of @classmethod. It wraps C-level slot functions (like dict.fromkeys) that need to receive cls as the first argument. The Python-level classmethod is a separate object type in funcobject.c.

mappingproxy

mappingproxy wraps an arbitrary mapping and raises TypeError on any mutation attempt. It is used for type.__dict__ and module __dict__ to prevent accidental modification through the read-only view.

// CPython: Objects/descrobject.c:1520 mappingproxy_setitem
static int
mappingproxy_setitem(mappingproxyobject *pp, PyObject *key, PyObject *value)
{
    PyErr_SetString(PyExc_TypeError,
                    "'mappingproxy' object does not support item assignment");
    return -1;
}

gopy notes

objects/property.go implements the property descriptor. objects/mapping_proxy.go implements mappingproxy. The classmethod and staticmethod descriptors are in objects/method.go. The chaining API (getter/setter/deleter) is ported.