Lib/operator.py / Modules/_operator.c (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Modules/_operator.c ↗

This annotation covers the higher-order operator helpers. See modules_operator2_detail for operator.add, operator.mul, operator.truth, and comparison operators.

Map

Lines	Symbol	Role
1-80	operator.attrgetter	Fast attribute accessor for key= functions
81-160	operator.itemgetter	Fast subscript accessor
161-240	operator.methodcaller	Call a named method with fixed args
241-400	operator.length_hint	__length_hint__ fallback for iterators

Reading

attrgetter

// CPython: Modules/_operator.c:580 attrgetter_new
static PyObject *
attrgetter_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    /* attrgetter('x') returns a callable f where f(obj) == obj.x
       attrgetter('x.y.z') chains: f(obj) == obj.x.y.z */
    attrgetterobject *ag = PyObject_GC_New(attrgetterobject, type);
    Py_ssize_t nattrs = PyTuple_GET_SIZE(args);
    ag->attr = ...; /* tuple of (split) attribute names */
    ...
}

static PyObject *
attrgetter_call(attrgetterobject *ag, PyObject *args, PyObject *kw)
{
    PyObject *obj = PyTuple_GET_ITEM(args, 0);
    /* For each dotted name, call getattr in sequence */
    for (int i = 0; i < nattrs; i++) {
        PyObject *name = ag->attr[i];
        obj = PyObject_GetAttr(obj, name);
    }
    return obj;
}

sorted(records, key=attrgetter('name')) is faster than lambda r: r.name because attrgetter avoids building a new Python frame for each call. attrgetter('a.b.c') is split at construction time, not on each call.

itemgetter

// CPython: Modules/_operator.c:680 itemgetter_call
static PyObject *
itemgetter_call(itemgetterobject *ig, PyObject *args, PyObject *kw)
{
    PyObject *obj = PyTuple_GET_ITEM(args, 0);
    if (ig->nitems == 1) {
        return PyObject_GetItem(obj, ig->item);
    }
    /* Multiple items: return a tuple */
    PyObject *result = PyTuple_New(ig->nitems);
    for (int i = 0; i < ig->nitems; i++) {
        PyTuple_SET_ITEM(result, i, PyObject_GetItem(obj, ig->items[i]));
    }
    return result;
}

sorted(data, key=itemgetter(2)) sorts by the third element. itemgetter(1, 3) returns a tuple of elements at indices 1 and 3, useful for multi-key sorting.

operator.length_hint

// CPython: Modules/_operator.c:880 op_length_hint
static PyObject *
op_length_hint(PyObject *module, PyObject *args)
{
    /* Return len(obj) if defined, else obj.__length_hint__() if defined,
       else the default value. */
    PyObject *obj, *default_value;
    Py_ssize_t hint = PyObject_LengthHint(obj, default_value);
    return PyLong_FromSsize_t(hint);
}

__length_hint__ is an optimization hint for iterators: list(it) pre-allocates based on length_hint to avoid repeated reallocs. The hint may be wrong; it is never trusted for correctness.

gopy notes

attrgetter is module/operator.AttrGetter in module/operator/module.go. Dotted names are split at construction into []string and each __call__ chains objects.GetAttr. itemgetter calls objects.GetItem. length_hint calls objects.LengthHint which checks __len__ then __length_hint__.