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.

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

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

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

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

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 raise TypeError and return NULL.

3.16 Raise !TypeError if callback is not callable, None, or NULL.

PyType_SUPPORTS_WEAKREFS for checking if ob is weakly referenceable.

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, NULL, this will raise TypeError and return NULL.

3.16 Raise !TypeError if callback is not callable, None, or NULL.

PyType_SUPPORTS_WEAKREFS for checking if ob is weakly referenceable.

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.

3.13

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.

3.14

This function is called by the ~PyTypeObject.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.

Return a pointer to an internal linked list of weak references to object. object must support weak references and must not be NULL.

This function is intended for internal use only. Do not access or modify the weak reference list through the returned pointer.

next

Clears the weakrefs for object without calling the callbacks.

This function is called by the ~PyTypeObject.tp_dealloc handler for types with finalizers (i.e., ~object.__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.

3.13