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copied!<p>Have you tried <a href="http://docs.python.org/library/gc.html#gc.set_debug" rel="noreferrer">gc.set_debug()</a> ?</p> <p>You need to ask yourself simple questions:</p> <ul> <li>Am I using objects with <code>__del__</code> methods? Do I absolutely, unequivocally, need them?</li> <li>Can I get reference cycles in my code? Can't we break these circles before getting rid of the objects?</li> </ul> <p>See, the main issue would be a cycle of objects containing <code>__del__</code> methods:</p> <pre><code>import gc class A(object): def __del__(self): print 'a deleted' if hasattr(self, 'b'): delattr(self, 'b') class B(object): def __init__(self, a): self.a = a def __del__(self): print 'b deleted' del self.a def createcycle(): a = A() b = B(a) a.b = b return a, b gc.set_debug(gc.DEBUG_LEAK) a, b = createcycle() # remove references del a, b # prints: ## gc: uncollectable <A 0x...> ## gc: uncollectable <B 0x...> ## gc: uncollectable <dict 0x...> ## gc: uncollectable <dict 0x...> gc.collect() # to solve this we break explicitely the cycles: a, b = createcycle() del a.b del a, b # objects are removed correctly: ## a deleted ## b deleted gc.collect() </code></pre> <p>I would really encourage you to flag objects / concepts that are cycling in your application and focus on their lifetime: when you don't need them anymore, do we have anything referencing it?</p> <p>Even for cycles without <code>__del__</code> methods, we can have an issue:</p> <pre><code>import gc # class without destructor class A(object): pass def createcycle(): # a -> b -> c # ^ | # ^<--<--<--| a = A() b = A() a.next = b c = A() b.next = c c.next = a return a, b, b gc.set_debug(gc.DEBUG_LEAK) a, b, c = createcycle() # since we have no __del__ methods, gc is able to collect the cycle: del a, b, c # no panic message, everything is collectable: ##gc: collectable <A 0x...> ##gc: collectable <A 0x...> ##gc: collectable <dict 0x...> ##gc: collectable <A 0x...> ##gc: collectable <dict 0x...> ##gc: collectable <dict 0x...> gc.collect() a, b, c = createcycle() # but as long as we keep an exterior ref to the cycle...: seen = dict() seen[a] = True # delete the cycle del a, b, c # nothing is collected gc.collect() </code></pre> <p>If you have to use "seen"-like dictionaries, or history, be careful that you keep only the actual data you need, and no external references to it.</p> <p>I'm a bit disappointed now by <code>set_debug</code>, I wish it could be configured to output data somewhere else than to stderr, but hopefully <a href="http://bugs.python.org/issue5851" rel="noreferrer">that should change soon</a>.</p>

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