1 .. highlightlang:: c 2 3 .. _weakrefobjects: 4 5 Weak Reference Objects 6 ---------------------- 7 8 Python supports *weak references* as first-class objects. There are two 9 specific object types which directly implement weak references. The first is a 10 simple reference object, and the second acts as a proxy for the original object 11 as 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 .. versionadded:: 2.2 19 20 21 .. c:function:: int PyWeakref_CheckRef(ob) 22 23 Return true if *ob* is a reference object. 24 25 .. versionadded:: 2.2 26 27 28 .. c:function:: int PyWeakref_CheckProxy(ob) 29 30 Return true if *ob* is a proxy object. 31 32 .. versionadded:: 2.2 33 34 35 .. c:function:: PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback) 36 37 Return a weak reference object for the object *ob*. This will always return 38 a new reference, but is not guaranteed to create a new object; an existing 39 reference object may be returned. The second parameter, *callback*, can be a 40 callable object that receives notification when *ob* is garbage collected; it 41 should accept a single parameter, which will be the weak reference object 42 itself. *callback* may also be ``None`` or *NULL*. If *ob* is not a 43 weakly-referencable object, or if *callback* is not callable, ``None``, or 44 *NULL*, this will return *NULL* and raise :exc:`TypeError`. 45 46 .. versionadded:: 2.2 47 48 49 .. c:function:: PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback) 50 51 Return a weak reference proxy object for the object *ob*. This will always 52 return a new reference, but is not guaranteed to create a new object; an 53 existing proxy object may be returned. The second parameter, *callback*, can 54 be a callable object that receives notification when *ob* is garbage 55 collected; it should accept a single parameter, which will be the weak 56 reference object itself. *callback* may also be ``None`` or *NULL*. If *ob* 57 is not a weakly-referencable object, or if *callback* is not callable, 58 ``None``, or *NULL*, this will return *NULL* and raise :exc:`TypeError`. 59 60 .. versionadded:: 2.2 61 62 63 .. c:function:: PyObject* PyWeakref_GetObject(PyObject *ref) 64 65 Return the referenced object from a weak reference, *ref*. If the referent is 66 no longer live, returns :const:`Py_None`. 67 68 .. versionadded:: 2.2 69 70 .. warning:: 71 72 This function returns a **borrowed reference** to the referenced object. 73 This means that you should always call :c:func:`Py_INCREF` on the object 74 except if you know that it cannot be destroyed while you are still 75 using it. 76 77 78 .. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref) 79 80 Similar to :c:func:`PyWeakref_GetObject`, but implemented as a macro that does no 81 error checking. 82 83 .. versionadded:: 2.2 84
