On Fri, Feb 18, 2011 at 8:10 PM, moerchendiser2k3 <googler.1.webmas...@spamgourmet.com> wrote: > Hi, I have some problems with Python and the garbage collection. In > the following piece of code I create a simple gargabe collection but I > am still wondering why the finalizers are never called - at least on > exit of Py they should be called somehow. What do I miss here? <code snippet involving circularly-referenced objects with __del__ methods snipped>
Read The Fine Manual (all emphases added): http://docs.python.org/reference/datamodel.html#object.__del__ : "***It is not guaranteed that __del__() methods are called for objects that still exist when the interpreter exits.***" "Note: [...] x.__del__() — [...] is only called when x‘s reference count reaches zero. Some common situations that may prevent the reference count of an object from going to zero include: circular references between objects [...] Circular references which are garbage are detected when the option cycle detector is enabled (it’s on by default), ***but can only be cleaned up if there are no Python-level __del__() methods involved***. Refer to the documentation for the `gc` module for more information about how __del__() methods are handled by the cycle detector, particularly the description of the `garbage` value." And following the pointer to gc.garbage's docs: http://docs.python.org/library/gc.html#gc.garbage : "Objects that have __del__() methods and are part of a reference cycle ***cause the entire reference cycle to be uncollectable*** [...] Python doesn’t collect such cycles automatically because, in general, it isn’t possible for Python to guess a safe order in which to run the __del__() methods. [...] It’s generally better to avoid the issue by not creating cycles containing objects with __del__() methods" Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
