On Mar 20, 8:12 pm, "andrew cooke" <and...@acooke.org> wrote: > Aaron Brady wrote: > > [...] > > > caveats and fragilities? If free software can do it, why isn't it all > > over the industry? What disqualifies it from solved-problem status? > > the two dominant virtual machines - .net and the jvm both handle circular > references with no problem whatever. this is standard in modern garbage > collection - go read a book on the subject (personally i like grune et > al's modern compiler design). it *is* a solved problem. if anything, > python is behind the curve, not ahead of it, but this may change with the > next generation of python implementations (pypy targets a variety of vms, > i think). > > as for the extra methods you suggest - why do you want to expose > implementation details in an api? that is not the normal aim of good > design. > > andrew
"Circular references ...can only be cleaned up if there are no Python- level __del__() methods involved." __del__ doc. "Python doesn’t collect ... cycles automatically because, in general, it isn’t possible for Python to guess a safe order in which to run the __del__() methods." gc.garbage doc. "Errors should never pass silently." -The Zen of Python I advance that cyclic objects should be notified when their external references go to zero, but their usual '__del__' is inappropriate. If objects implement a __del__ method, they can choose to implement a '__gc_cycle__' method, and then just drop the specified attribute. It needn't be called on every object in the cycle, either; once it's called on one object, another object's normal __del__ may be safely called. Output, unproduced: >>> del x In X.__gc_cycle__, 'other' attribute. Deleting... In Y.__del__. In X.__del__. >>> The actual backend of CPython requires garbage-collected container types to implement tp_inquiry and tp_clear methods, but user-defined types apparently aren't required to conform. Supporting Cyclic Garbage Collection http://docs.python.org/3.0/c-api/gcsupport.html -- http://mail.python.org/mailman/listinfo/python-list
