Edit File: weakref.txt
.. highlightlang:: c .. _weakrefobjects: Weak Reference Objects ---------------------- Python supports *weak references* as first-class objects. There are two specific object types which directly implement weak references. The first is a simple reference object, and the second acts as a proxy for the original object as much as it can. .. c:function:: int PyWeakref_Check(ob) Return true if *ob* is either a reference or proxy object. .. versionadded:: 2.2 .. c:function:: int PyWeakref_CheckRef(ob) Return true if *ob* is a reference object. .. versionadded:: 2.2 .. c:function:: int PyWeakref_CheckProxy(ob) Return true if *ob* is a proxy object. .. versionadded:: 2.2 .. c:function:: PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback) Return a weak reference object for the object *ob*. This will always return a new reference, but is not guaranteed to create a new object; an existing reference object may be returned. The second parameter, *callback*, can be a callable object that receives notification when *ob* is garbage collected; it should accept a single parameter, which will be the weak reference object itself. *callback* may also be ``None`` or *NULL*. If *ob* is not a weakly-referencable object, or if *callback* is not callable, ``None``, or *NULL*, this will return *NULL* and raise :exc:`TypeError`. .. versionadded:: 2.2 .. c:function:: PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback) Return a weak reference proxy object for the object *ob*. This will always return a new reference, but is not guaranteed to create a new object; an existing proxy object may be returned. The second parameter, *callback*, can be a callable object that receives notification when *ob* is garbage collected; it should accept a single parameter, which will be the weak reference object itself. *callback* may also be ``None`` or *NULL*. If *ob* is not a weakly-referencable object, or if *callback* is not callable, ``None``, or *NULL*, this will return *NULL* and raise :exc:`TypeError`. .. versionadded:: 2.2 .. c:function:: PyObject* PyWeakref_GetObject(PyObject *ref) Return the referenced object from a weak reference, *ref*. If the referent is no longer live, returns :const:`Py_None`. .. versionadded:: 2.2 .. warning:: This function returns a **borrowed reference** to the referenced object. This means that you should always call :c:func:`Py_INCREF` on the object except if you know that it cannot be destroyed while you are still using it. .. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref) Similar to :c:func:`PyWeakref_GetObject`, but implemented as a macro that does no error checking. .. versionadded:: 2.2