[issue9417] Declaring a class creates circular references

[Ray.Allen]

Ray.Allen <ysj.ray at gmail.com> added the comment:

krisvale:

> What about my suggestion of simply providing a convention on how to disable links manually, similar to how minidom.document does it with an "unlink" method?  If these cases are documented, then there shouldn't be any extra bother to do so.
We could provide an builtin unlink() function that calls any __unlink__ special method if present.


Maybe through this way such problems can be solved, but it seems it's not graceful and pythonic enough. The reason such an "unlink" method appears in xml.dom.minidom is because usually large xml document can eat up so much memory that we had to do something to make the memory garbaged sooner. But adding this as a standard __unlink__ method and requiring explicitly call the unlink() method make it similar as using c & c++, which require explicitly memory release. 

Besides, as you mentioned, "exposes an implementation detail of C python", it's better that the object reference mechanism be fully controlled by python core and not be awared by users at all. That is also one of the purposes of designing python. 

I prefer terry's idea, which suggests adding a metaclass that produces rc-free class to stdlib. These class should behave almost the same as the ones "type" metaclass produces. In order not to introduce the slower lookup, we can also add a little differences on usage of such classes, for example, internally store mro list without the class itself, but construct a full mro list when getting the __mro__ attribute, and different "super" implementation, since explicitly getting the mro is not so common in practice.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9417>
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