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python-3.7.4-docs-html/_sources/c-api/weakref.rst.txt

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+.. 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.
+
+
+.. c:function:: int PyWeakref_CheckRef(ob)
+
+   Return true if *ob* is a reference object.
+
+
+.. c:function:: int PyWeakref_CheckProxy(ob)
+
+   Return true if *ob* is a proxy object.
+
+
+.. 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`.
+
+
+.. 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`.
+
+
+.. 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`.
+
+   .. note::
+
+      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.