Weak Reference Objects — Python documentation

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.

int PyWeakref_Check(ob)

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

int PyWeakref_CheckRef(ob)

Return true if ob is a reference object.

int PyWeakref_CheckProxy(ob)

Return true if ob is a proxy object.

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 TypeError.

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 TypeError.

PyObject *PyWeakref_GetObject(PyObject *ref)

Return the referenced object from a weak reference, ref. If the referent is no longer live, returns Py_None.

Note

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)

Similar to PyWeakref_GetObject(), but implemented as a macro that does no error checking.