| msg186122 - (view) |
Author: Mark Dickinson (mark.dickinson) *  |
Date: 2013-04-06 12:54 |
| It would be nice to be able to access the callback of a weakref as an attribute on the weakref itself. For example: Python 3.4.0a0 (default:2bf154ca43c6+, Apr 6 2013, 13:31:29) [GCC 4.2.1 (Apple Inc. build 5664)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import weakref >>> x = {1, 2, 3} >>> ref = weakref.ref(x, lambda ref: print("done")) >>> ref.__callback__ <function at 0x1004f56d0> >>> del x done >>> ref.__callback__ # Returns None I encountered this while writing a tool to show graphs of Python objects and their references to each other: I wanted to be able to annotate each edge of the graph. For something like a function, it's easy to use introspection to compare the reference target with f.__code__, f.__annotations__, etc. For a weakref, I couldn't find an easy way to retrieve the callback (or even determine whether there *was* a callback associated to the weakref). One can do a "gc.get_referents" call and hope that if there's exactly one object returned it's the callback, but that won't work so well with weakref.ref subclasses. Patch attached: it has tests but no doc updates as yet. |
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| msg186124 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2013-04-06 13:43 |
| Sounds fine to me. |
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| msg186125 - (view) |
Author: Benjamin Peterson (benjamin.peterson) * |
Date: 2013-04-06 13:48 |
| Instead of a getset, I think you just use a read-only T_OBJECT member. |
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| msg186132 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2013-04-06 15:04 |
| Ah yes; that's easier. New patch including doc updates. |
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| msg186151 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2013-04-06 19:27 |
| "del x" will not be enough on non-refcounted implementations. |
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| msg186154 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2013-04-06 19:31 |
| True: I'm not sure what to do about that---there are other tests in that test module that also rely on del resulting in immediate cleanup. I'm not sure what other implementations are currently doing with this test module. I could mark the new test as cpython only, or add a gc.collect (but I'm not sure if the latter is enough, either). |
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| msg186155 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2013-04-06 19:31 |
| Ah, then we can probably keep using the same style. |
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| msg186655 - (view) |
Author: Terry J. Reedy (terry.reedy) * |
Date: 2013-04-12 17:41 |
| > there are other tests in that test module that also rely on del resulting in immediate cleanup I would mark them all as 'cpython-only', since they are. Other implementation must be omitting this test module, ignoring its failures, or patching out the specific tests. |
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| msg186665 - (view) |
Author: Richard Oudkerk (sbt) * |
Date: 2013-04-12 18:52 |
| > I could mark the new test as cpython only, or add a gc.collect (but I'm > not sure if the latter is enough, either). test.support.gc_collect() should work on non-refcounted implementations. |
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| msg186668 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2013-04-12 19:04 |
| Ah, test.support.gc_collect looks useful. Thanks! |
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| msg186722 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2013-04-13 14:45 |
| New changeset 9e7d31b04d78 by Mark Dickinson in branch 'default': Issue #17643: Add __callback__ attribute to weakref.ref. http://hg.python.org/cpython/rev/9e7d31b04d78 |
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| msg186723 - (view) |
Author: Mark Dickinson (mark.dickinson) * |
Date: 2013-04-13 14:47 |
| Committed, using support.gc_collect for the test that requires garbage collection. Thanks for the reviews! |
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