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    <p>About the only reason you should ever use <code>__del__</code> is to help the garbage collector collect more garbage. For instance, if you are implementing something like the <code>ctypes</code> module that attaches shared libraries to the running process, it makes sense to unload those libraries when the last reference to it is collected, to allow its address space to be used for something else.</p> <p>For managing <em>other</em> kinds of resources, you almost certainly don't want to have anything to do with the garbage collector. The correct tool for this is <a href="http://docs.python.org/reference/datamodel.html#with-statement-context-managers" rel="noreferrer">context managers</a>. Unlike languages such as C++ or Ada where variable scope is used for RAII, python uses the <code>with</code> statement, along with an object that has an <code>__enter__</code> and <code>__exit__</code> method. Many built in python types use this exact mechanism to make sure finalization steps actually occur:</p> <pre><code>&gt;&gt;&gt; x = file("foo", 'w') &gt;&gt;&gt; x.closed False &gt;&gt;&gt; with x: ... x.write("bar") ... &gt;&gt;&gt; x.closed True </code></pre> <p>This is also valuable from the point of view of the zen of python:</p> <blockquote> <p>Explicit is better than implicit.</p> </blockquote> <p>because it is clear that cleanup is occuring, it is explicitly written that way. This is much better than the case of cleanup happening "magically" when some hidden variable (the reference count, if one exists, and it doesn't in PyPy or IronPython or Jython) reaches some particular value, maybe.</p>
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    1. POhow soon is `__del__` called after reference count drops to zero?
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    1. COWeakref callbacks are a much better way of implementing the kind of cleanup that you suggest `__del__` methods are for, because they don't prevent cleanup of cycles. The only reason `__del__` exists as it does is because it predates considerations of non-refcount Python implementations as well as weakrefs.
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      1. USThomas Wouters
 

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