Ref Util
effortless weakrefs to objects, methods, and functions with annotations
Preamble
There is a fairly common need to reference some data in the callback of a weakref when the object is being garbage collected. This package provides a simple interface for creating new annotated, slotted, reference types, which subclass weakref.ref in the standard library.
Documentation consists of this README and the code.
Table of Contents
Technologies
- python >=2.5
Example
Code
import collections
import refutil
Subscription = collections.namedtuple('Subscription', ['callback', 'topic', 'subscription_id'])
SubscriptionWeakRef = refutil.reftype('SubscriptionWeakRef', ['subscription_id'])
class Subscriptions:
def __init__(self):
self.subscriptions = {}
def _weak_remove_callback(self, ref):
print('weak callback triggered')
self.remove(ref.subscription_id)
def add(self, topic, callback, subscription_id):
# make a weak reference to the callback, so that it will be garbage
# collected, but store the subscription_id in the reference
# and then add a method callback, which will be weakly referenced as well,
# to handle when the callback is garbage collected
wrcallback = SubscriptionWeakRef(
callback,
self._weak_remove_callback,
subscription_id=subscription_id
)
subscription = Subscription(
topic=topic,
callback=wrcallback,
subscription_id=subscription_id
)
self.subscriptions[subscription_id] = subscription
print('subscription added', subscription_id)
def remove(self, subscription_id):
print('subscription removed', subscription_id)
del self.subscriptions[subscription_id]
subs = Subscriptions()
def my_callback():
pass
subs.add('topic', my_callback, 'sub-1')
subs.add('topic', my_callback, 'sub-2')
print(subs.subscriptions)
print('deleting callback')
del my_callback
print(subs.subscriptions)Output
subscription added sub-1
subscription added sub-2
{'sub-1': Subscription(callback=<weakref at 0x01874300; to 'function' at 0x01873C48 (my_callback)>, topic='topic', subscription_id='sub-1'), 'sub-2': Subscription(callback=<weakref at 0x018743F0; to 'function' at 0x01873C48 (my_callback)>, topic='topic', subscription_id='sub-2')}
deleting callback
weak callback triggered
subscription removed sub-2
weak callback triggered
subscription removed sub-1
{}
