1.. highlight:: c
2
3.. _weakrefobjects:
4
5Weak Reference Objects
6----------------------
7
8Python supports *weak references* as first-class objects.  There are two
9specific object types which directly implement weak references.  The first is a
10simple reference object, and the second acts as a proxy for the original object
11as much as it can.
12
13
14.. c:function:: int PyWeakref_Check(ob)
15
16   Return true if *ob* is either a reference or proxy object.
17
18
19.. c:function:: int PyWeakref_CheckRef(ob)
20
21   Return true if *ob* is a reference object.
22
23
24.. c:function:: int PyWeakref_CheckProxy(ob)
25
26   Return true if *ob* is a proxy object.
27
28
29.. c:function:: PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback)
30
31   Return a weak reference object for the object *ob*.  This will always return
32   a new reference, but is not guaranteed to create a new object; an existing
33   reference object may be returned.  The second parameter, *callback*, can be a
34   callable object that receives notification when *ob* is garbage collected; it
35   should accept a single parameter, which will be the weak reference object
36   itself. *callback* may also be ``None`` or ``NULL``.  If *ob* is not a
37   weakly-referencable object, or if *callback* is not callable, ``None``, or
38   ``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
39
40
41.. c:function:: PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
42
43   Return a weak reference proxy object for the object *ob*.  This will always
44   return a new reference, but is not guaranteed to create a new object; an
45   existing proxy object may be returned.  The second parameter, *callback*, can
46   be a callable object that receives notification when *ob* is garbage
47   collected; it should accept a single parameter, which will be the weak
48   reference object itself. *callback* may also be ``None`` or ``NULL``.  If *ob*
49   is not a weakly-referencable object, or if *callback* is not callable,
50   ``None``, or ``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
51
52
53.. c:function:: PyObject* PyWeakref_GetObject(PyObject *ref)
54
55   Return the referenced object from a weak reference, *ref*.  If the referent is
56   no longer live, returns :const:`Py_None`.
57
58   .. note::
59
60      This function returns a **borrowed reference** to the referenced object.
61      This means that you should always call :c:func:`Py_INCREF` on the object
62      except if you know that it cannot be destroyed while you are still
63      using it.
64
65
66.. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref)
67
68   Similar to :c:func:`PyWeakref_GetObject`, but implemented as a macro that does no
69   error checking.
70