source: vendor/python/2.5/Objects/cellobject.c

/* Cell object implementation */

#include "Python.h"

PyObject *
PyCell_New(PyObject *obj)
{
        PyCellObject *op;

        op = (PyCellObject *)PyObject_GC_New(PyCellObject, &PyCell_Type);
        if (op == NULL)
                return NULL;
        op->ob_ref = obj;
        Py_XINCREF(obj);

        _PyObject_GC_TRACK(op);
        return (PyObject *)op;
}

PyObject *
PyCell_Get(PyObject *op)
{
        if (!PyCell_Check(op)) {
                PyErr_BadInternalCall();
                return NULL;
        }
        Py_XINCREF(((PyCellObject*)op)->ob_ref);
        return PyCell_GET(op);
}

int
PyCell_Set(PyObject *op, PyObject *obj)
{
        if (!PyCell_Check(op)) {
                PyErr_BadInternalCall();
                return -1;
        }
        Py_XDECREF(((PyCellObject*)op)->ob_ref);
        Py_XINCREF(obj);
        PyCell_SET(op, obj);
        return 0;
}

static void
cell_dealloc(PyCellObject *op)
{
        _PyObject_GC_UNTRACK(op);
        Py_XDECREF(op->ob_ref);
        PyObject_GC_Del(op);
}

static int
cell_compare(PyCellObject *a, PyCellObject *b)
{
        if (a->ob_ref == NULL) {
                if (b->ob_ref == NULL)
                        return 0;
                return -1;
        } else if (b->ob_ref == NULL)
                return 1;
        return PyObject_Compare(a->ob_ref, b->ob_ref);
}

static PyObject *
cell_repr(PyCellObject *op)
{
        if (op->ob_ref == NULL)
                return PyString_FromFormat("<cell at %p: empty>", op);

        return PyString_FromFormat("<cell at %p: %.80s object at %p>",
                                   op, op->ob_ref->ob_type->tp_name,
                                   op->ob_ref);
}

static int
cell_traverse(PyCellObject *op, visitproc visit, void *arg)
{
        Py_VISIT(op->ob_ref);
        return 0;
}

static int
cell_clear(PyCellObject *op)
{
        Py_CLEAR(op->ob_ref);
        return 0;
}

static PyObject *
cell_get_contents(PyCellObject *op, void *closure)
{
        Py_XINCREF(op->ob_ref);
        return op->ob_ref;
}

static PyGetSetDef cell_getsetlist[] = {
        {"cell_contents", (getter)cell_get_contents, NULL},
        {NULL} /* sentinel */
};

PyTypeObject PyCell_Type = {
        PyObject_HEAD_INIT(&PyType_Type)
        0,
        "cell",
        sizeof(PyCellObject),
        0,
        (destructor)cell_dealloc,               /* tp_dealloc */
        0,                                      /* tp_print */
        0,                                      /* tp_getattr */
        0,                                      /* tp_setattr */
        (cmpfunc)cell_compare,                  /* tp_compare */
        (reprfunc)cell_repr,                    /* tp_repr */
        0,                                      /* tp_as_number */
        0,                                      /* tp_as_sequence */
        0,                                      /* tp_as_mapping */
        0,                                      /* tp_hash */
        0,                                      /* tp_call */
        0,                                      /* tp_str */
        PyObject_GenericGetAttr,                /* tp_getattro */
        0,                                      /* tp_setattro */
        0,                                      /* tp_as_buffer */
        Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
        0,                                      /* tp_doc */
        (traverseproc)cell_traverse,            /* tp_traverse */
        (inquiry)cell_clear,                    /* tp_clear */
        0,                                      /* tp_richcompare */
        0,                                      /* tp_weaklistoffset */
        0,                                      /* tp_iter */
        0,                                      /* tp_iternext */
        0,                                      /* tp_methods */
        0,                                      /* tp_members */
        cell_getsetlist,                        /* tp_getset */
};