# 弱参照オブジェクト

Python は 弱参照 を第一級オブジェクト (first-class object) としてサポートします。弱参照を直接実装する二種類の固有のオブジェクト型があります。第一は単純な参照オブジェクトで、第二はオリジナルのオブジェクトに対して可能な限りプロキシとして振舞うオブジェクトです。

int PyWeakref_Check(PyObject *ob)

  Return non-zero if ob is either a reference or proxy object. This function always succeeds.

int PyWeakref_CheckRef(PyObject *ob)

  Return non-zero if ob is a reference object or a subclass of the reference type. This function always succeeds.

int PyWeakref_CheckRefExact(PyObject *ob)

  Return non-zero if ob is a reference object, but not a subclass of the reference type. This function always succeeds.

int PyWeakref_CheckProxy(PyObject *ob)

  Return non-zero if ob is a proxy object. This function always succeeds.

PyObject *PyWeakref_NewRef(PyObject *ob, PyObject *callback)
  戻り値: 新しい参照。 次に属します: 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 referenceable object, or if callback is not callable, `None`, or `NULL`, this will return `NULL` and raise `TypeError`.

  参考

  `PyType_SUPPORTS_WEAKREFS()` for checking if ob is weakly referenceable.

PyObject *PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
  戻り値: 新しい参照。 次に属します: 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 referenceable object, or if callback is not callable, `None`, or `NULL`, this will return `NULL` and raise `TypeError`.

  参考

  `PyType_SUPPORTS_WEAKREFS()` for checking if ob is weakly referenceable.

int PyWeakref_GetRef(PyObject *ref, PyObject **pobj)
  次に属します: Stable ABI (バージョン 3.13 より).

  Get a strong reference to the referenced object from a weak reference, ref, into *pobj.

  - On success, set *pobj to a new strong reference to the referenced object and return 1.

  - If the reference is dead, set *pobj to `NULL` and return 0.

  - On error, raise an exception and return -1.

  Added in version 3.13.

PyObject *PyWeakref_GetObject(PyObject *ref)
  戻り値: 借用参照。 次に属します: Stable ABI.

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

  注釈

  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.

  Deprecated since version 3.13, will be removed in version 3.15: Use `PyWeakref_GetRef()` instead.

PyObject *PyWeakref_GET_OBJECT(PyObject *ref)
  戻り値: 借用参照。

  Similar to `PyWeakref_GetObject()`, but does no error checking.

  Deprecated since version 3.13, will be removed in version 3.15: Use `PyWeakref_GetRef()` instead.

int PyWeakref_IsDead(PyObject *ref)

  Test if the weak reference ref is dead. Returns 1 if the reference is dead, 0 if it is alive, and -1 with an error set if ref is not a weak reference object.

  Added in version 3.14.

void PyObject_ClearWeakRefs(PyObject *object)
  次に属します: 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.

void PyUnstable_Object_ClearWeakRefsNoCallbacks(PyObject *object)
  これは Unstable APIです。マイナーリリースで予告なく変更されることがあります。

  Clears the weakrefs for object without calling the callbacks.

  This function is called by the `tp_dealloc` handler for types with finalizers (i.e., `__del__()`). The handler for those objects first calls `PyObject_ClearWeakRefs()` to clear weakrefs and call their callbacks, then the finalizer, and finally this function to clear any weakrefs that may have been created by the finalizer.

  In most circumstances, it's more appropriate to use `PyObject_ClearWeakRefs()` to clear weakrefs instead of this function.

  Added in version 3.13.