Objects/dictobject.c (part 2)

cpython 3.14 @ ab2d84fe1023/Objects/dictobject.c ↗

This annotation covers dict views, update/merge, and compact dict version tracking in Objects/dictobject.c. For the hash table internals, insertion, and lookup see the objects_dictobject annotation.

Map

Lines	Symbol	Role
1-400	dict_keys_iter, dict_values_iter, dict_items_iter	View iterators
401-800	dictkeys_type, dictvalues_type, dictitems_type	View objects with len/contains/iter
801-1200	dict_keys set algebra	__and__, __or__, __sub__, __xor__ on keys view
1201-1600	dict_merge, dict_update_common	Merge a mapping or iterable of pairs
1601-2000	dict_copy, dict_fromkeys	Shallow copy and class method constructor
2001-5600	Version tracking, shared keys	ma_version_tag, split/combined table

Reading

Dict views

dict.keys(), dict.values(), dict.items() return view objects that reflect the current contents of the dict. Views support len(), iteration, and in membership. The keys() view additionally supports set operations since dict keys are guaranteed to be unique.

// CPython: Objects/dictobject.c:3820 dictkeys_contains
static int
dictkeys_contains(dictkeysviewobject *dkv, PyObject *obj)
{
    return PyDict_Contains(dkv->dv_dict, obj);
}

ma_version_tag

Every dict mutation increments ma_version_tag, a 64-bit monotonic counter. This allows code that caches the dict state to detect changes without comparing the dict contents. The specialization machinery uses this to invalidate type attribute caches.

Split and combined dicts

Class instance dicts share a PyDictKeysObject (the key table) among all instances of the same class. The first modification splits the shared keys, creating a private copy. This "split-combined" optimisation reduces memory use for objects with consistent attribute sets.

dict_merge

dict_merge(a, b, override) handles both Mapping objects (by calling keys() + __getitem__) and sequences of 2-tuples. The override flag controls whether existing keys in a are overwritten.

gopy notes

objects/dict.go implements the core dict. Dict views (dict_keys, dict_values, dict_items) are in objects/dict_iter.go. ma_version_tag is not yet tracked; the split/combined optimisation is not implemented.