Skip to main content

Objects/descrobject.c — mappingproxyobject (part 2)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/descrobject.c

This annotation covers mappingproxy read operations and merge. See objects_mapping_proxy_detail for mappingproxy.__new__, __setattr__ restriction, and type.__dict__ wiring.

Map​

LinesSymbolRole
1-80mappingproxy.__getitem__Delegate proxy[key] to the underlying mapping
81-180keys / values / itemsForward to the wrapped dict
181-280__contains__ / getPresence check and default retrieval
281-400__or__ / __ror__Merge: `proxy

Reading​

mappingproxy.__getitem__​

// CPython: Objects/descrobject.c:1120 mappingproxy_getitem
static PyObject *
mappingproxy_getitem(mappingproxyobject *pp, PyObject *key)
{
    return PyObject_GetItem(pp->dict, key);
}

type.__dict__['method'] dispatches through mappingproxy.__getitem__. The proxy wraps any mapping, not just dicts: types.MappingProxyType({'a': 1}) works with any Mapping.

keys / values / items​

// CPython: Objects/descrobject.c:1180 mappingproxy_keys
static PyObject *
mappingproxy_keys(mappingproxyobject *pp, PyObject *Py_UNUSED(ignored))
{
    return PyMapping_Keys(pp->dict);
}

type.__dict__.keys() returns the underlying dict's keys view. The proxy forwards all read methods to pp->dict. Because tp_as_mapping->mp_subscript is set but mp_ass_subscript is NULL, proxy[key] = value raises TypeError: 'mappingproxy' object does not support item assignment.

__or__​

// CPython: Objects/descrobject.c:1260 mappingproxy_or
static PyObject *
mappingproxy_or(PyObject *self, PyObject *other)
{
    mappingproxyobject *pp = (mappingproxyobject *)self;
    /* proxy | other: create a new dict by merging */
    return PyNumber_Or(pp->dict, other);
}

type.__dict__ | {'extra': 1} returns a plain dict. The | operator is read-only: it creates a new dict rather than modifying the proxy. |= is not supported.

gopy notes​

mappingproxy.__getitem__ is objects.MappingProxyGetItem in objects/mapping_proxy.go. keys/values/items delegate to objects.DictKeys, objects.DictValues, objects.DictItems. __or__ calls objects.DictOr to merge into a new dict.