#!/usr/bin/env python # encoding: utf-8 # # Copyright (c) 2010 Doug Hellmann. All rights reserved. # """Show the objects with references to a given object. """ #end_pymotw_header import gc import pprint class Graph(object): def __init__(self, name): self.name = name self.next = None def set_next(self, next): print 'Linking nodes %s.next = %s' % (self, next) self.next = next def __repr__(self): return '%s(%s)' % (self.__class__.__name__, self.name) def __del__(self): print '%s.__del__()' % self # Construct a graph cycle one = Graph('one') two = Graph('two') three = Graph('three') one.set_next(two) two.set_next(three) three.set_next(one) # Remove references to the graph nodes in this module's namespace one = two = three = None # Collecting now keeps the objects as uncollectable print print 'Collecting...' n = gc.collect() print 'Unreachable objects:', n print 'Remaining Garbage:', pprint.pprint(gc.garbage) # Break the cycle print print 'Breaking the cycle' gc.garbage[0].set_next(None) print 'Removing references in gc.garbage' del gc.garbage[:] # Now the objects are removed print print 'Collecting...' n = gc.collect() print 'Unreachable objects:', n print 'Remaining Garbage:', pprint.pprint(gc.garbage)