.. 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.

.. cfunction:: int PyWeakref_Check(ob)

   Return true if *ob* is either a reference or proxy object.

   .. versionadded:: 2.2

.. cfunction:: int PyWeakref_CheckRef(ob)

   Return true if *ob* is a reference object.

   .. versionadded:: 2.2

.. cfunction:: int PyWeakref_CheckProxy(ob)

   Return true if *ob* is a proxy object.

   .. versionadded:: 2.2

.. cfunction:: 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

.. cfunction:: 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

.. cfunction:: PyObject* PyWeakref_GetObject(PyObject *ref)

   Return the referenced object from a weak reference, *ref*.  If the referent is

   no longer live, returns ``None``.

   .. versionadded:: 2.2

.. cfunction:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref)

   Similar to :cfunc:`PyWeakref_GetObject`, but implemented as a macro that does no

   error checking.

   .. versionadded:: 2.2