Objects/namespaceobject.c

cpython 3.14 @ ab2d84fe1023/Objects/namespaceobject.c ↗

Objects/namespaceobject.c implements types.SimpleNamespace, a lightweight object whose attributes live in an internal __dict__. It is simpler than a full user-defined class because it has no __slots__, no inheritance chain beyond object, and no custom metaclass. argparse.Namespace is the most common caller in the standard library.

Map

Lines	Symbol	Role
1-30	_PyNamespaceObject	Struct with PyObject_HEAD and ns_dict
31-100	namespace_new, namespace_init	Constructor accepting keyword arguments
101-160	namespace_getattro, namespace_setattro	Attribute access via ns_dict
161-220	namespace_repr	Repr using ns_dict items in insertion order
221-260	namespace_richcompare	Equality via dict comparison
261-290	PyNamespace_Type	Type object

Reading

namespace_init: keyword-only construction

SimpleNamespace accepts only keyword arguments. Each keyword becomes an attribute backed by an entry in ns_dict. Positional arguments raise TypeError.

// CPython: Objects/namespaceobject.c:55 namespace_init
static int
namespace_init(PyObject *self, PyObject *args, PyObject *kwds)
{
    _PyNamespaceObject *ns = (_PyNamespaceObject *)self;
    if (PyTuple_GET_SIZE(args) != 0) {
        PyErr_SetString(PyExc_TypeError,
                        "no positional arguments expected");
        return -1;
    }
    if (kwds == NULL)
        return 0;
    return PyDict_Merge(ns->ns_dict, kwds, 1);
}

Attribute access through ns_dict

namespace_getattro delegates to PyObject_GenericGetAttr, which looks in ns_dict as the instance dictionary. namespace_setattro calls PyObject_GenericSetAttr, also backed by ns_dict. There is no descriptor machinery beyond what object provides.

// CPython: Objects/namespaceobject.c:120 namespace_getattro
static PyObject *
namespace_getattro(PyObject *self, PyObject *name)
{
    return PyObject_GenericGetAttr(self, name);
}

namespace_repr: ordered attribute display

repr(ns) iterates ns_dict in insertion order and formats each key-value pair. It uses a _PyUnicodeWriter to build the result string efficiently.

// CPython: Objects/namespaceobject.c:170 namespace_repr
static PyObject *
namespace_repr(PyObject *self)
{
    _PyNamespaceObject *ns = (_PyNamespaceObject *)self;
    ...
    /* format: namespace(key=value, ...) */

gopy notes

types.SimpleNamespace is partially covered by objects/namespace.go in gopy. The Go implementation wraps a map[string]*Object and exposes GetAttr/SetAttr backed by that map. The namespace_repr ordered output is not yet implemented; repr currently produces an unordered result.

CPython 3.14 changes

3.14 added __replace__ to SimpleNamespace (analogous to dataclasses.replace), allowing keyword-argument-based copy-with-overrides without subclassing.