Modules/_weakref.c

#include "Python.h"
#include "structmember.h"


typedef struct _PyWeakReference PyWeakReference;

struct _PyWeakReference {
    PyObject_HEAD
    PyObject *wr_object;
    PyObject *wr_callback;
    PyWeakReference *wr_prev;
    PyWeakReference *wr_next;
};


#define GET_WEAKREFS_LISTPTR(o) \
        ((PyWeakReference **) PyObject_GET_WEAKREFS_LISTPTR(o))

static PyObject *
ReferenceError;

static PyWeakReference *
free_list = NULL;

staticforward PyTypeObject
PyWeakReference_Type;

static PyWeakReference *
new_weakref(void)
{
    PyWeakReference *result;

    if (free_list != NULL) {
        result = free_list;
        free_list = result->wr_next;
        result->ob_type = &PyWeakReference_Type;
        _Py_NewReference(result);
    }
    else {
        result = PyObject_NEW(PyWeakReference, &PyWeakReference_Type);
    }
    return result;
}


/* This function clears the passed-in reference and removes it from the
 * list of weak references for the referent.  This is the only code that
 * removes an item from the doubly-linked list of weak references for an
 * object; it is also responsible for clearing the callback slot.
 */
static void
clear_weakref(PyWeakReference *self)
{
    PyObject *callback = self->wr_callback;

    if (self->wr_object != Py_None) {
        PyWeakReference **list = GET_WEAKREFS_LISTPTR(self->wr_object);

        if (*list == self)
            *list = self->wr_next;
        self->wr_object = Py_None;
        self->wr_callback = NULL;
        if (self->wr_prev != NULL)
            self->wr_prev->wr_next = self->wr_next;
        if (self->wr_next != NULL)
            self->wr_next->wr_prev = self->wr_prev;
        self->wr_prev = NULL;
        self->wr_next = NULL;
        Py_XDECREF(callback);
    }
}


static void
weakref_dealloc(PyWeakReference *self)
{
    clear_weakref(self);
    PyObject_GC_Fini((PyObject *)self);
    self->wr_next = free_list;
    free_list = self;
}


static int
gc_traverse(PyWeakReference *self, visitproc visit, void *arg)
{
    if (self->wr_callback != NULL)
        return visit(self->wr_callback, arg);
    return 0;
}


static int
gc_clear(PyWeakReference *self)
{
    clear_weakref(self);
    return 0;
}


static PyObject *
weakref_call(PyWeakReference *self, PyObject *args, PyObject *kw)
{
    static char *argnames[] = {NULL};

    if (PyArg_ParseTupleAndKeywords(args, kw, ":__call__", argnames)) {
        PyObject *object = self->wr_object;
        Py_INCREF(object);
        return (object);
    }
    return NULL;
}


static PyObject *
weakref_repr(PyWeakReference *self)
{
    char buffer[256];
    if (self->wr_object == Py_None) {
        sprintf(buffer, "<weakref at %lx; dead>",
                (long)(self));
    }
    else {
        sprintf(buffer, "<weakref at %#lx; to '%s' at %#lx>",
                (long)(self), self->wr_object->ob_type->tp_name,
                (long)(self->wr_object));
    }
    return PyString_FromString(buffer);
}


statichere PyTypeObject
PyWeakReference_Type = {
    PyObject_HEAD_INIT(NULL)
    0,
    "weakref",
    sizeof(PyWeakReference) + PyGC_HEAD_SIZE,
    0,
    (destructor)weakref_dealloc,/*tp_dealloc*/
    0,	                        /*tp_print*/
    0,                          /*tp_getattr*/
    0,                          /*tp_setattr*/
    0,	                        /*tp_compare*/
    (reprfunc)weakref_repr,     /*tp_repr*/
    0,                          /*tp_as_number*/
    0,                          /*tp_as_sequence*/
    0,                          /*tp_as_mapping*/
    0,                          /*tp_hash*/
    (ternaryfunc)weakref_call,  /*tp_call*/
    0,                          /*tp_str*/
    0,                          /*tp_getattro*/
    0,                          /*tp_setattro*/
    0,                          /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_GC,
    0,                          /*tp_doc*/
    (traverseproc)gc_traverse,  /*tp_traverse*/
    (inquiry)gc_clear,          /*tp_clear*/
};


static int
proxy_checkref(PyWeakReference *proxy)
{
    if (proxy->wr_object == Py_None) {
        PyErr_SetString(ReferenceError,
                        "weakly-referenced object no longer exists");
        return 0;
    }
    return 1;
}


#define WRAP_UNARY(method, generic) \
    static PyObject * \
    method(PyWeakReference *proxy) { \
        if (!proxy_checkref(proxy)) { \
            return NULL; \
        } \
        return generic(proxy->wr_object); \
    }

#define WRAP_BINARY(method, generic) \
    static PyObject * \
    method(PyWeakReference *proxy, PyObject *v) { \
        if (!proxy_checkref(proxy)) { \
            return NULL; \
        } \
        return generic(proxy->wr_object, v); \
    }

#define WRAP_TERNARY(method, generic) \
    static PyObject * \
    method(PyWeakReference *proxy, PyObject *v, PyObject *w) { \
        if (!proxy_checkref(proxy)) { \
            return NULL; \
	} \
        return generic(proxy->wr_object, v, w); \
    }


/* direct slots */

WRAP_BINARY(proxy_getattr, PyObject_GetAttr)
WRAP_UNARY(proxy_str, PyObject_Str)
WRAP_TERNARY(proxy_call, PyEval_CallObjectWithKeywords)

static int
proxy_print(PyWeakReference *proxy, FILE *fp, int flags)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PyObject_Print(proxy->wr_object, fp, flags);
}

static PyObject *
proxy_repr(PyWeakReference *proxy)
{
    char buf[160];
    sprintf(buf, "<weakref at %p to %.100s at %p>", proxy,
            proxy->wr_object->ob_type->tp_name, proxy->wr_object);
    return PyString_FromString(buf);
}


static int
proxy_setattr(PyWeakReference *proxy, PyObject *name, PyObject *value)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PyObject_SetAttr(proxy->wr_object, name, value);
}

static int
proxy_compare(PyWeakReference *proxy, PyObject *v)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PyObject_Compare(proxy->wr_object, v);
}

/* number slots */
WRAP_BINARY(proxy_add, PyNumber_Add)
WRAP_BINARY(proxy_sub, PyNumber_Subtract)
WRAP_BINARY(proxy_mul, PyNumber_Multiply)
WRAP_BINARY(proxy_div, PyNumber_Divide)
WRAP_BINARY(proxy_mod, PyNumber_Remainder)
WRAP_BINARY(proxy_divmod, PyNumber_Divmod)
WRAP_TERNARY(proxy_pow, PyNumber_Power)
WRAP_UNARY(proxy_neg, PyNumber_Negative)
WRAP_UNARY(proxy_pos, PyNumber_Positive)
WRAP_UNARY(proxy_abs, PyNumber_Absolute)
WRAP_UNARY(proxy_invert, PyNumber_Invert)
WRAP_BINARY(proxy_lshift, PyNumber_Lshift)
WRAP_BINARY(proxy_rshift, PyNumber_Rshift)
WRAP_BINARY(proxy_and, PyNumber_And)
WRAP_BINARY(proxy_xor, PyNumber_Xor)
WRAP_BINARY(proxy_or, PyNumber_Or)
WRAP_UNARY(proxy_int, PyNumber_Int)
WRAP_UNARY(proxy_long, PyNumber_Long)
WRAP_UNARY(proxy_float, PyNumber_Float)
WRAP_BINARY(proxy_iadd, PyNumber_InPlaceAdd)
WRAP_BINARY(proxy_isub, PyNumber_InPlaceSubtract)
WRAP_BINARY(proxy_imul, PyNumber_InPlaceMultiply)
WRAP_BINARY(proxy_idiv, PyNumber_InPlaceDivide)
WRAP_BINARY(proxy_imod, PyNumber_InPlaceRemainder)
WRAP_TERNARY(proxy_ipow, PyNumber_InPlacePower)
WRAP_BINARY(proxy_ilshift, PyNumber_InPlaceLshift)
WRAP_BINARY(proxy_irshift, PyNumber_InPlaceRshift)
WRAP_BINARY(proxy_iand, PyNumber_InPlaceAnd)
WRAP_BINARY(proxy_ixor, PyNumber_InPlaceXor)
WRAP_BINARY(proxy_ior, PyNumber_InPlaceOr)

static int 
proxy_nonzero(PyWeakReference *proxy)
{
    PyObject *o = proxy->wr_object;
    if (!proxy_checkref(proxy))
        return 1;
    if (o->ob_type->tp_as_number &&
        o->ob_type->tp_as_number->nb_nonzero)
        return (*o->ob_type->tp_as_number->nb_nonzero)(o);
    else
        return 1;
}

/* sequence slots */

static PyObject *
proxy_slice(PyWeakReference *proxy, int i, int j)
{
    if (!proxy_checkref(proxy))
        return NULL;
    return PySequence_GetSlice(proxy->wr_object, i, j);
}

static int
proxy_ass_slice(PyWeakReference *proxy, int i, int j, PyObject *value)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PySequence_SetSlice(proxy->wr_object, i, j, value);
}

static int
proxy_contains(PyWeakReference *proxy, PyObject *value)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PySequence_Contains(proxy->wr_object, value);
}


/* mapping slots */

static int
proxy_length(PyWeakReference *proxy)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PyObject_Length(proxy->wr_object);
}

WRAP_BINARY(proxy_getitem, PyObject_GetItem)

static int
proxy_setitem(PyWeakReference *proxy, PyObject *key, PyObject *value)
{
    if (!proxy_checkref(proxy))
        return -1;
    return PyObject_SetItem(proxy->wr_object, key, value);
}


static PyNumberMethods proxy_as_number = {
    (binaryfunc)proxy_add,      /*nb_add*/
    (binaryfunc)proxy_sub,      /*nb_subtract*/
    (binaryfunc)proxy_mul,      /*nb_multiply*/
    (binaryfunc)proxy_div,      /*nb_divide*/
    (binaryfunc)proxy_mod,      /*nb_remainder*/
    (binaryfunc)proxy_divmod,   /*nb_divmod*/
    (ternaryfunc)proxy_pow,     /*nb_power*/
    (unaryfunc)proxy_neg,       /*nb_negative*/
    (unaryfunc)proxy_pos,       /*nb_positive*/
    (unaryfunc)proxy_abs,       /*nb_absolute*/
    (inquiry)proxy_nonzero,     /*nb_nonzero*/
    (unaryfunc)proxy_invert,    /*nb_invert*/
    (binaryfunc)proxy_lshift,   /*nb_lshift*/
    (binaryfunc)proxy_rshift,   /*nb_rshift*/
    (binaryfunc)proxy_and,      /*nb_and*/
    (binaryfunc)proxy_xor,      /*nb_xor*/
    (binaryfunc)proxy_or,       /*nb_or*/
    (coercion)0,                /*nb_coerce*/
    (unaryfunc)proxy_int,       /*nb_int*/
    (unaryfunc)proxy_long,      /*nb_long*/
    (unaryfunc)proxy_float,     /*nb_float*/
    (unaryfunc)0,               /*nb_oct*/
    (unaryfunc)0,               /*nb_hex*/
    (binaryfunc)proxy_iadd,     /*nb_inplace_add*/
    (binaryfunc)proxy_isub,     /*nb_inplace_subtract*/
    (binaryfunc)proxy_imul,     /*nb_inplace_multiply*/
    (binaryfunc)proxy_idiv,     /*nb_inplace_divide*/
    (binaryfunc)proxy_imod,     /*nb_inplace_remainder*/
    (ternaryfunc)proxy_ipow,    /*nb_inplace_power*/
    (binaryfunc)proxy_ilshift,  /*nb_inplace_lshift*/
    (binaryfunc)proxy_irshift,  /*nb_inplace_rshift*/
    (binaryfunc)proxy_iand,     /*nb_inplace_and*/
    (binaryfunc)proxy_ixor,     /*nb_inplace_xor*/
    (binaryfunc)proxy_ior,      /*nb_inplace_or*/
};

static PySequenceMethods proxy_as_sequence = {
    (inquiry)proxy_length,      /*sq_length*/
    0,                          /*sq_concat*/
    0,                          /*sq_repeat*/
    0,                          /*sq_item*/
    (intintargfunc)proxy_slice, /*sq_slice*/
    0,                          /*sq_ass_item*/
    (intintobjargproc)proxy_ass_slice, /*sq_ass_slice*/
    (objobjproc)proxy_contains, /* sq_contains */
};

static PyMappingMethods proxy_as_mapping = {
    (inquiry)proxy_length,      /*mp_length*/
    (binaryfunc)proxy_getitem,  /*mp_subscript*/
    (objobjargproc)proxy_setitem, /*mp_ass_subscript*/
};


static PyTypeObject
PyWeakProxy_Type = {
    PyObject_HEAD_INIT(NULL)
    0,
    "weakproxy",
    sizeof(PyWeakReference) + PyGC_HEAD_SIZE,
    0,
    /* methods */
    (destructor)weakref_dealloc,/*tp_dealloc*/
    (printfunc)proxy_print,     /*tp_print*/
    0,				/*tp_getattr*/
    0, 				/*tp_setattr*/
    (cmpfunc)proxy_compare,	/*tp_compare*/
    (unaryfunc)proxy_repr,	/*tp_repr*/
    &proxy_as_number,		/*tp_as_number*/
    &proxy_as_sequence,		/*tp_as_sequence*/
    &proxy_as_mapping,		/*tp_as_mapping*/
    0,	                        /*tp_hash*/
    (ternaryfunc)0,	        /*tp_call*/
    (unaryfunc)proxy_str,	/*tp_str*/
    (getattrofunc)proxy_getattr,/*tp_getattro*/
    (setattrofunc)proxy_setattr,/*tp_setattro*/
    0,				/*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_GC
    |Py_TPFLAGS_CHECKTYPES,     /*tp_flags*/
    0,                          /*tp_doc*/
    (traverseproc)gc_traverse,  /*tp_traverse*/
    (inquiry)gc_clear,          /*tp_clear*/
};


static PyTypeObject
PyWeakCallableProxy_Type = {
    PyObject_HEAD_INIT(NULL)
    0,
    "weakcallableproxy",
    sizeof(PyWeakReference) + PyGC_HEAD_SIZE,
    0,
    /* methods */
    (destructor)weakref_dealloc,/*tp_dealloc*/
    (printfunc)proxy_print,     /*tp_print*/
    0,				/*tp_getattr*/
    0, 				/*tp_setattr*/
    (cmpfunc)proxy_compare,	/*tp_compare*/
    (unaryfunc)proxy_repr,	/*tp_repr*/
    &proxy_as_number,		/*tp_as_number*/
    &proxy_as_sequence,		/*tp_as_sequence*/
    &proxy_as_mapping,		/*tp_as_mapping*/
    0,	                        /*tp_hash*/
    (ternaryfunc)proxy_call,	/*tp_call*/
    (unaryfunc)proxy_str,	/*tp_str*/
    (getattrofunc)proxy_getattr,/*tp_getattro*/
    (setattrofunc)proxy_setattr,/*tp_setattro*/
    0,				/*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_GC
    |Py_TPFLAGS_CHECKTYPES,     /*tp_flags*/
    0,                          /*tp_doc*/
    (traverseproc)gc_traverse,  /*tp_traverse*/
    (inquiry)gc_clear,          /*tp_clear*/
};


static long
getweakrefcount(PyWeakReference *head)
{
    long count = 0;

    while (head != NULL) {
        ++count;
        head = head->wr_next;
    }
    return count;
}


static PyObject *
weakref_getweakrefcount(PyObject *self, PyObject *args)
{
    PyObject *result = NULL;
    PyObject *object;

    if (PyArg_ParseTuple(args, "O:getweakrefcount", &object)) {
        if (PyType_SUPPORTS_WEAKREFS(object->ob_type)) {
            PyWeakReference **list = GET_WEAKREFS_LISTPTR(object);

            result = PyInt_FromLong(getweakrefcount(*list));
        }
        else
            result = PyInt_FromLong(0);
    }
    return result;
}


static PyObject *
weakref_getweakrefs(PyObject *self, PyObject *args)
{
    PyObject *result = NULL;
    PyObject *object;

    if (PyArg_ParseTuple(args, "O:getweakrefs", &object)) {
        if (PyType_SUPPORTS_WEAKREFS(object->ob_type)) {
            PyWeakReference **list = GET_WEAKREFS_LISTPTR(object);
            long count = getweakrefcount(*list);

            result = PyList_New(count);
            if (result != NULL) {
                PyWeakReference *current = *list;
                long i;
                for (i = 0; i < count; ++i) {
                    PyList_SET_ITEM(result, i, (PyObject *) current);
                    Py_INCREF(current);
                    current = current->wr_next;
                }
            }
        }
        else {
            result = PyList_New(0);
        }
    }
    return result;
}


/* Given the head of an object's list of weak references, extract the
 * two callback-less refs (ref and proxy).  Used to determine if the
 * shared references exist and to determine the back link for newly
 * inserted references.
 */
static void
get_basic_refs(PyWeakReference *head,
               PyWeakReference **refp, PyWeakReference **proxyp)
{
    *refp = NULL;
    *proxyp = NULL;

    if (head != NULL && head->wr_callback == NULL) {
        if (head->ob_type == &PyWeakReference_Type) {
            *refp = head;
            head = head->wr_next;
        }
        if (head != NULL && head->wr_callback == NULL) {
            *proxyp = head;
            head = head->wr_next;
        }
    }
}

/* Insert 'newref' in the list after 'prev'.  Both must be non-NULL. */
static void
insert_after(PyWeakReference *newref, PyWeakReference *prev)
{
    newref->wr_prev = prev;
    newref->wr_next = prev->wr_next;
    if (prev->wr_next != NULL)
        prev->wr_next->wr_prev = newref;
    prev->wr_next = newref;
}

/* Insert 'newref' at the head of the list; 'list' points to the variable
 * that stores the head.
 */
static void
insert_head(PyWeakReference *newref, PyWeakReference **list)
{
    PyWeakReference *next = *list;

    newref->wr_prev = NULL;
    newref->wr_next = next;
    if (next != NULL)
        next->wr_prev = newref;
    *list = newref;
}


static PyObject *
weakref_ref(PyObject *self, PyObject *args)
{
    PyObject *object;
    PyObject *callback = NULL;
    PyWeakReference *result = NULL;

    if (PyArg_ParseTuple(args, "O|O:new", &object, &callback)) {
        PyWeakReference **list;
        PyWeakReference *ref, *proxy;

        if (!PyType_SUPPORTS_WEAKREFS(object->ob_type)) {
            PyErr_Format(PyExc_TypeError,
                         "'%s' objects are not weakly referencable",
                         object->ob_type->tp_name);
            return NULL;
        }
        list = GET_WEAKREFS_LISTPTR(object);
        get_basic_refs(*list, &ref, &proxy);
        if (callback == NULL) {
            /* return existing weak reference if it exists */
            result = ref;
            Py_XINCREF(result);
        }
        if (result == NULL) {
            result = new_weakref();
            if (result != NULL) {
                Py_XINCREF(callback);
                result->wr_callback = callback;
                result->wr_object = object;
                if (callback == NULL) {
                    insert_head(result, list);
                }
                else {
                    PyWeakReference *prev = (proxy == NULL) ? ref : proxy;

                    if (prev == NULL)
                        insert_head(result, list);
                    else
                        insert_after(result, prev);
                }
                PyObject_GC_Init((PyObject *) result);
            }
        }
    }
    return (PyObject *) result;
}


static PyObject *
weakref_proxy(PyObject *self, PyObject *args)
{
    PyObject *object;
    PyObject *callback = NULL;
    PyWeakReference *result = NULL;

    if (PyArg_ParseTuple(args, "O|O:new", &object, &callback)) {
        PyWeakReference **list;
        PyWeakReference *ref, *proxy;

        if (!PyType_SUPPORTS_WEAKREFS(object->ob_type)) {
            PyErr_Format(PyExc_TypeError,
                         "'%s' objects are not weakly referencable",
                         object->ob_type->tp_name);
            return NULL;
        }
        list = GET_WEAKREFS_LISTPTR(object);
        get_basic_refs(*list, &ref, &proxy);
        if (callback == NULL) {
            /* attempt to return an existing weak reference if it exists */
            result = proxy;
            Py_XINCREF(result);
        }
        if (result == NULL) {
            result = new_weakref();
            if (result != NULL) {
                PyWeakReference *prev;

                if (PyCallable_Check(object))
                    result->ob_type = &PyWeakCallableProxy_Type;
                else
                    result->ob_type = &PyWeakProxy_Type;
                result->wr_object = object;
                Py_XINCREF(callback);
                result->wr_callback = callback;
                if (callback == NULL)
                    prev = ref;
                else
                    prev = (proxy == NULL) ? ref : proxy;

                if (prev == NULL)
                    insert_head(result, list);
                else
                    insert_after(result, prev);
                PyObject_GC_Init((PyObject *) result);
            }
        }
    }
    return (PyObject *) result;
}


/* This is the implementation of the PyObject_ClearWeakRefs() function; it
 * is installed in the init_weakref() function.  It is called by the
 * tp_dealloc handler to clear weak references.
 *
 * This returns true if the object should be deallocated, and false if the
 * object is resurrected and deallocation should be aborted.
 *
 * This iterates through the weak references for 'object' and calls callbacks
 * until one resurrects the object, at which point it stops invalidating
 * weak references and returns false.
 */
static int
cleanup_helper(PyObject *object)
{
    PyWeakReference **list;

    if (object == NULL
        || !PyType_SUPPORTS_WEAKREFS(object->ob_type)
        || object->ob_refcnt != 0) {
        PyErr_BadInternalCall();
        /* not sure what we should return here */
        return 1;
    }
    list = GET_WEAKREFS_LISTPTR(object);
    while (*list != NULL) {
        PyWeakReference *current = *list;
        PyObject *callback = current->wr_callback;

        Py_XINCREF(callback);
        clear_weakref(current);
        if (callback != NULL) {
            PyObject *cbresult;

            cbresult = PyObject_CallFunction(callback, "O", current);
            if (cbresult == NULL)
                PyErr_WriteUnraisable(callback);
            else
                Py_DECREF(cbresult);
            Py_DECREF(callback);
        }
    }
    return (object->ob_refcnt > 0 ? 0 : 1);
}


static PyMethodDef
weakref_functions[] =  {
    {"getweakrefcount", weakref_getweakrefcount,        METH_VARARGS,
     "getweakrefcount(object) -- return the number of weak references\n"
     "to 'object'."},
    {"getweakrefs",     weakref_getweakrefs,            METH_VARARGS,
     "getweakrefs(object) -- return a list of all weak reference objects\n"
     "that point to 'object'."},
    {"proxy",           weakref_proxy,	                METH_VARARGS,
     "proxy(object[, callback]) -- create a proxy object that weakly\n"
     "references 'object'.  'callback', if given, is called with a\n"
     "reference to 'object' when it is about to be finalized."},
    {"ref",             weakref_ref,                    METH_VARARGS,
     "new(object[, callback]) -- create a weak reference to 'object';\n"
     "when 'object' is finalized, 'callback' will be called and passed\n"
     "a reference to 'object'."},
    {NULL, NULL, 0, NULL}
};


void
init_weakref(void)
{
    PyObject *m;

    PyWeakReference_Type.ob_type = &PyType_Type;
    PyWeakProxy_Type.ob_type = &PyType_Type;
    PyWeakCallableProxy_Type.ob_type = &PyType_Type;
    m = Py_InitModule3("_weakref", weakref_functions,
                       "Weak-reference support module.");
    if (m != NULL) {
        PyObject_ClearWeakRefs = cleanup_helper;
        Py_INCREF(&PyWeakReference_Type);
        PyModule_AddObject(m, "ReferenceType",
                           (PyObject *) &PyWeakReference_Type);
        Py_INCREF(&PyWeakProxy_Type);
        PyModule_AddObject(m, "ProxyType",
                           (PyObject *) &PyWeakProxy_Type);
        Py_INCREF(&PyWeakCallableProxy_Type);
        PyModule_AddObject(m, "CallableProxyType",
                           (PyObject *) &PyWeakCallableProxy_Type);
        ReferenceError = PyErr_NewException("weakref.ReferenceError",
                                            PyExc_RuntimeError, NULL);
        if (ReferenceError != NULL)
            PyModule_AddObject(m, "ReferenceError", ReferenceError);
    }
}