Weak Reference Objects — Python 2.7.18 documentation

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# 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.

  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.