cpython/Objects/dict-common.h

#ifndef Py_DICT_COMMON_H
#define Py_DICT_COMMON_H

typedef struct {
    /* Cached hash code of me_key. */
    Py_hash_t me_hash;
    PyObject *me_key;
    PyObject *me_value; /* This field is only meaningful for combined tables */
} PyDictKeyEntry;

/* dict_lookup_func() returns index of entry which can be used like DK_ENTRIES(dk)[index].
 * -1 when no entry found, -3 when compare raises error.
 */
typedef Py_ssize_t (*dict_lookup_func)
(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject ***value_addr,
 Py_ssize_t *hashpos);

#define DKIX_EMPTY (-1)
#define DKIX_DUMMY (-2)  /* Used internally */
#define DKIX_ERROR (-3)

/* See dictobject.c for actual layout of DictKeysObject */
struct _dictkeysobject {
    Py_ssize_t dk_refcnt;
    Py_ssize_t dk_size;
    dict_lookup_func dk_lookup;
    Py_ssize_t dk_usable;
    Py_ssize_t dk_nentries;  /* How many entries are used. */
    char dk_indices[8];      /* dynamically sized. 8 is minimum. */
};

#endif