weakref_valuedict.py

#!/usr/bin/env python


import gc
from pprint import pprint
import weakref

gc.set_debug(gc.DEBUG_LEAK)


class ExpensiveObject(object):
    def __init__(self, name):
        self.name = name

    def __repr__(self):
        return 'ExpensiveObject(%s)' % self.name

    def __del__(self):
        print ' (Deleting %s)' % self


def demo(cache_factory):
    all_refs = {}
    print 'CACHE TYPE:', cache_factory
    cache = cache_factory()
    for name in ['one', 'two', 'three']:
        o = ExpensiveObject(name)
        cache[name] = o
        all_refs[name] = o
        del o  # decref

    print '    all_refs =',
    pprint(all_refs)
    print '\n Before, cache contains:', cache.keys()
    for name, value in cache.items():
        print ' %s = %s' % (name, value)
        del value  # decref

    # Remove all references to the objects except the cache
    print '\n Cleanup:'
    del all_refs
    gc.collect()

    print '\n After, cache contains:', cache.keys()
    for name, value in cache.items():
        print '     %s = %s' % (name, value)
    print ' demo returning'
    return

demo(dict)
print

demo(weakref.WeakValueDictionary)