| msg48132 - (view) |
Author: Greg Chapman (glchapman) |
Date: 2005-04-03 15:29 |
| In Python 2.4, you can weakref instances of classic classes but not the classes themselves. Attached is a patch which adds weakref support to classic classes. |
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| msg48133 - (view) |
Author: Raymond Hettinger (rhettinger) *  |
Date: 2005-04-10 16:02 |
| Logged In: YES user_id=80475 I'm curious why you would ever want to do this. It is somewhat rare to delete a class reference and, I presume, rarer still to need a weak-reference to such a class. |
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| msg48134 - (view) |
Author: Greg Chapman (glchapman) |
Date: 2005-04-10 17:05 |
| Logged In: YES user_id=86307 Here's my use case. I've been experimenting with the multimethods module written by David Mertz (part of his gnosis utilities). This uses mros from a declared signature and from the actual parameter types to determine which overload to call. Classic classes don't have an mro, so I needed to calculate one to accomodate them. Having done so, I wanted to cache it. The best solution might be the one I'm using now, which is simply to assign the calculated mro to a __mro__ attribute of the classic class. However, it seemed better to me to use an external cache, rather than modifying the class. I wanted this external cache to be a WeakKeyDictionary, because, if a module containing a classic class is reloaded, I didn't want the old version of the class kept alive solely by my cache (it avoided a reference cycle with the mro itself by storing a list with the first element set to None; then, when fetched, copying the list and putting the class in the copy's first element). Anyway, feel free to reject this. It was so easy to do, I just thought I'd go ahead and post it in case the lack was simply an oversight. |
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| msg48135 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2005-04-10 18:51 |
| Logged In: YES user_id=80475 Be sure to add Py_TPFLAGS_HAVE_WEAKREFS to tp_flags. Beef-up the unittest. See test_weakref() in test.test_deque.py for an example. Add classic classes to the list of weak referencables in libweakref.tex. Include a \versionadded tag. Add an entry to Misc/NEWS. |
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| msg48136 - (view) |
Author: Greg Chapman (glchapman) |
Date: 2005-04-10 19:47 |
| Logged In: YES user_id=86307 Ah, I see, not so easy to do it properly. Fair enough. One quick question though: Py_TPFLAGS_HAVE_WEAKREFS is included in Py_TPFLAGS_DEFAULT. I didn't include it explicitly because of that and because neither of the other two types in classobject.c explicitly uses it (though I see other types do explicitly use it). So are PyInstance_Type and PyMethod_Type wrong? (Should I include a change to their definitions?) |
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| msg48137 - (view) |
Author: Greg Chapman (glchapman) |
Date: 2005-07-09 14:26 |
| Logged In: YES user_id=86307 Well, I'd been meaning to get around to finishing this, but here it is three months later, and I haven't found (or made) the time. So I'm just going to close this as Rejected. |
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| msg48138 - (view) |
Author: Georg Brandl (georg.brandl) * |
Date: 2005-07-09 15:29 |
| Logged In: YES user_id=1188172 Changing to Postponed, as the new functionality as such wasn't rejected. |
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