mirror of https://github.com/python/cpython
80 lines
3.0 KiB
ReStructuredText
80 lines
3.0 KiB
ReStructuredText
.. highlight:: c
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.. _weakrefobjects:
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Weak Reference Objects
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----------------------
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Python supports *weak references* as first-class objects. There are two
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specific object types which directly implement weak references. The first is a
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simple reference object, and the second acts as a proxy for the original object
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as much as it can.
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.. c:function:: int PyWeakref_Check(ob)
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Return true if *ob* is either a reference or proxy object. This function
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always succeeds.
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.. c:function:: int PyWeakref_CheckRef(ob)
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Return true if *ob* is a reference object. This function always succeeds.
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.. c:function:: int PyWeakref_CheckProxy(ob)
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Return true if *ob* is a proxy object. This function always succeeds.
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.. c:function:: PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback)
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Return a weak reference object for the object *ob*. This will always return
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a new reference, but is not guaranteed to create a new object; an existing
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reference object may be returned. The second parameter, *callback*, can be a
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callable object that receives notification when *ob* is garbage collected; it
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should accept a single parameter, which will be the weak reference object
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itself. *callback* may also be ``None`` or ``NULL``. If *ob* is not a
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weakly referencable object, or if *callback* is not callable, ``None``, or
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``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
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.. c:function:: PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
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Return a weak reference proxy object for the object *ob*. This will always
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return a new reference, but is not guaranteed to create a new object; an
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existing proxy object may be returned. The second parameter, *callback*, can
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be a callable object that receives notification when *ob* is garbage
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collected; it should accept a single parameter, which will be the weak
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reference object itself. *callback* may also be ``None`` or ``NULL``. If *ob*
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is not a weakly referencable object, or if *callback* is not callable,
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``None``, or ``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
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.. c:function:: PyObject* PyWeakref_GetObject(PyObject *ref)
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Return the referenced object from a weak reference, *ref*. If the referent is
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no longer live, returns :const:`Py_None`.
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.. note::
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This function returns a :term:`borrowed reference` to the referenced object.
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This means that you should always call :c:func:`Py_INCREF` on the object
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except when it cannot be destroyed before the last usage of the borrowed
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reference.
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.. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref)
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Similar to :c:func:`PyWeakref_GetObject`, but does no error checking.
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.. c:function:: void PyObject_ClearWeakRefs(PyObject *object)
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This function is called by the :c:member:`~PyTypeObject.tp_dealloc` handler
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to clear weak references.
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This iterates through the weak references for *object* and calls callbacks
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for those references which have one. It returns when all callbacks have
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been attempted.
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