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.
int PyWeakref_Check(ob)
Return true if ob is either a reference or proxy object.
New in version 2.2.
int PyWeakref_CheckRef(ob)
Return true if ob is a reference object.
New in version 2.2.
int PyWeakref_CheckProxy(ob)
Return true if ob is a proxy object.
New in version 2.2.
PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback)
Return value: New reference.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 TypeError.
New in version 2.2.
PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
Return value: New reference.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 TypeError.
New in version 2.2.
PyObject* PyWeakref_GetObject(PyObject *ref)
Return value: Borrowed reference.Return the referenced object from a weak reference, ref. If the referent is
no longer live, returns Py_None.
New in version 2.2.
Warning
This function returns a borrowed reference to the referenced object.
This means that you should always call Py_INCREF() on the object
except if you know that it cannot be destroyed while you are still
using it.
PyObject* PyWeakref_GET_OBJECT(PyObject *ref)
Return value: Borrowed reference.Similar to PyWeakref_GetObject(), but implemented as a macro that does no
error checking.
New in version 2.2.