Weak Reference Objects — Python 3.10.19 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. This function always succeeds.

int `PyWeakref_CheckRef`(ob)

  Return true if ob is a reference object. This function always succeeds.

int `PyWeakref_CheckProxy`(ob)

  Return true if ob is a proxy object. This function always succeeds.

PyObject *`PyWeakref_NewRef`(PyObject *ob, PyObject *callback)
  Return value: New reference. Part of the Stable ABI.

  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 value: New reference. Part of the Stable ABI.

  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 value: Borrowed reference. Part of the Stable ABI.

  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 when it cannot be destroyed before the last usage of the borrowed reference.

PyObject *`PyWeakref_GET_OBJECT`(PyObject *ref)
  Return value: Borrowed reference.

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

void `PyObject_ClearWeakRefs`(PyObject *object)
  Part of the Stable ABI.

  This function is called by the `tp_dealloc` handler to clear weak references.

  This iterates through the weak references for object and calls callbacks for those references which have one. It returns when all callbacks have been attempted.