Objects/listobject.c (part 9)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/listobject.c ↗

This annotation covers list search and copy operations. See objects_listobject8_detail for Timsort.

Map

Lines	Symbol	Role
1-80	list.__contains__	Linear search with __eq__
81-160	list.index	Return first index of value
161-240	list.count	Count occurrences
241-320	list.copy	Shallow copy
321-400	list.clear	Remove all elements

Reading

list.__contains__

// CPython: Objects/listobject.c:440 list_contains
static int
list_contains(PyListObject *a, PyObject *el)
{
    for (Py_ssize_t i = 0; i < Py_SIZE(a); i++) {
        PyObject *item = a->ob_item[i];
        if (item == el) return 1;  /* Identity fast path */
        int cmp = PyObject_RichCompareBool(item, el, Py_EQ);
        if (cmp > 0) return 1;
        if (cmp < 0) return -1;  /* Error */
    }
    return 0;
}

Identity check first (item == el): if el is interned or the same object, no comparison is needed. __eq__ is called for the general case. Short-circuits on the first match.

list.index

// CPython: Objects/listobject.c:480 list_index_impl
static PyObject *
list_index_impl(PyListObject *self, PyObject *value, Py_ssize_t start,
                Py_ssize_t stop)
{
    for (Py_ssize_t i = start; i < stop; i++) {
        int cmp = PyObject_RichCompareBool(self->ob_item[i], value, Py_EQ);
        if (cmp > 0) return PyLong_FromSsize_t(i);
        if (cmp < 0) return NULL;
    }
    PyErr_Format(PyExc_ValueError, "%R is not in list", value);
    return NULL;
}

list.index(x, start, stop) limits the search to [start, stop). Raises ValueError if not found.

list.copy

// CPython: Objects/listobject.c:560 list_copy_impl
static PyObject *
list_copy_impl(PyListObject *self)
{
    /* Equivalent to self[:] */
    return list_slice(self, 0, Py_SIZE(self));
}

static PyObject *
list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
{
    PyListObject *np = (PyListObject *)PyList_New(ihigh - ilow);
    for (Py_ssize_t i = 0; i < n; i++) {
        np->ob_item[i] = Py_NewRef(a->ob_item[ilow + i]);
    }
    return (PyObject *)np;
}

list.copy() is a shallow copy: a new list with Py_NewRef on each element. Equivalent to lst[:]. For a deep copy, use copy.deepcopy.

gopy notes

list.__contains__ is objects.ListContains in objects/list.go. It checks pointer equality first, then calls objects.RichCompareBool(item, el, EQ). list.copy calls objects.ListSlice(lst, 0, len(lst.Items)). list.clear sets lst.Items = lst.Items[:0].