Python/ceval.c (part 54)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers STORE_ATTR specializations for instance attribute writes. See python_ceval53_detail for COMPARE_OP specializations.

Map

Lines	Symbol	Role
1-80	STORE_ATTR_SLOT	Write to a fixed-offset C slot
81-160	STORE_ATTR_WITH_HINT	Instance dict write with cached index
161-260	STORE_ATTR_INSTANCE_VALUE	Inline values dict (Python 3.12+ split dict)
261-360	STORE_ATTR (generic)	Fallback: __setattr__ dispatch
361-500	DELETE_ATTR	Remove an attribute

Reading

STORE_ATTR_SLOT

// CPython: Python/ceval.c:5080 STORE_ATTR_SLOT
inst(STORE_ATTR_SLOT, (unused/2, owner, value --)) {
    DEOPT_IF(!PyObject_TypeHasFeature(Py_TYPE(owner), Py_TPFLAGS_HEAPTYPE));
    Py_ssize_t offset = cache->index;
    PyObject *old_value = *(PyObject **)((char *)owner + offset);
    *(PyObject **)((char *)owner + offset) = Py_NewRef(value);
    Py_XDECREF(old_value);
    DECREF_INPUTS();
    DISPATCH();
}

For __slots__ attributes and C extension members: write directly to a byte offset in the object struct. No dict involved.

STORE_ATTR_WITH_HINT

// CPython: Python/ceval.c:5140 STORE_ATTR_WITH_HINT
inst(STORE_ATTR_WITH_HINT, (unused/2, owner, value --)) {
    DEOPT_IF(!PyObject_TypeHasFeature(Py_TYPE(owner), Py_TPFLAGS_MANAGED_DICT));
    PyDictObject *dict = _PyObject_GetManagedDict(owner);
    DEOPT_IF(dict == NULL);
    DEOPT_IF(dict->ma_version_tag != cache->version);
    Py_ssize_t hint = cache->index;
    PyObject *name = GETITEM(FRAME_CO_NAMES, cache->name_or_flag);
    if (_PyDict_SetItemHint(dict, name, hint, value) != hint) {
        DEOPT_IF(true);
    }
    DECREF_INPUTS();
    DISPATCH();
}

The hint is the expected index in the instance dict. If the dict version matches, the write goes directly to the expected slot without hashing. Common for self.x = val patterns.

STORE_ATTR_INSTANCE_VALUE

// CPython: Python/ceval.c:5200 STORE_ATTR_INSTANCE_VALUE
inst(STORE_ATTR_INSTANCE_VALUE, (unused/2, owner, value --)) {
    /* Python 3.12+ inline values: small number of instance attrs stored
       directly in the object, not in a separate dict */
    DEOPT_IF(!PyObject_TypeHasFeature(Py_TYPE(owner), Py_TPFLAGS_MANAGED_DICT));
    _PyObjectDict_SetItem(Py_TYPE(owner), _PyObject_ManagedDictPointer(owner),
                          cache->index, value);
    DECREF_INPUTS();
    DISPATCH();
}

Python 3.12 introduced inline values: the first few instance attributes are stored directly in the object alongside the type pointer, avoiding a dict allocation for simple classes.

gopy notes

STORE_ATTR_SLOT writes via unsafe.Pointer arithmetic to a cached byte offset in vm/eval_simple.go. STORE_ATTR_WITH_HINT calls objects.DictSetHint. STORE_ATTR_INSTANCE_VALUE uses objects.InstanceSetInline which writes to instance.InlineValues[index], a small pre-allocated slice on each instance.