Issue535444
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Created on 2002-03-26 22:13 by pje, last changed 2022-04-10 16:05 by admin. This issue is now closed.
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msg9995 - (view) | Author: PJ Eby (pje) * ![]() |
Date: 2002-03-26 22:13 | |
Using super() in a classmethod breaks in Python 2.2. Apparently, when super looks up an attribute from the __mro__ sequence, it calls the found descriptor's __get__ with the descriptor itself as the 'type' argument, which breaks horribly with class methods (which always binds to the type argument). Presumably, the fix is to pass a NULL type argument, which should work with the recent fixes to the classmethod's __get__ logic. In other words, this code in the super_getattro function Objects/typeobject.c: tmp = f(res, su->obj, res); should probably actually read: tmp = f(res, su->obj, NULL); |
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msg9996 - (view) | Author: Martin v. Löwis (loewis) * ![]() |
Date: 2002-03-27 12:26 | |
Logged In: YES user_id=21627 Can you give an example of how to break it? Please also report what your example does when you run it. |
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msg9997 - (view) | Author: PJ Eby (pje) * ![]() |
Date: 2002-03-27 13:06 | |
Logged In: YES user_id=56214 class cm1(object): def cmm(klass): print klass cmm = classmethod(cmm) class cm2(cm1): def cmm(klass): super(cm2,klass).cmm() cmm = classmethod(cmm) cm2.cmm() The above code prints "<classmethod object at 0x00A9B930>", demonstrating that super(cm2,klass).cmm is bound improperly. (It should print <class '__main__.cm2'>, analagous to how calling cm1.cmm() directly prints <class '__main__.cm1'>.) You can more specifically verify this like so: >>> cm1.cmm.im_self <class '__main__.cm1'> >>> cm2.cmm.im_self <class '__main__.cm2'> >>> super(cm2,cm2).cmm.im_self <classmethod object at 0x00A9B930> >>> The last item's im_self should of course be <class '__main__.cm2'>. As I said, the problem is that super_getattro incorrectly asks the classmethod descriptor to bind to *itself*, rather than to a type. Note that if you use the pure Python example version of "super" defined in the python.org/2.2/descrintro.html document, the above examples work correctly as long as you use a version of Python that has the "classmethod core dump" problem fixed. However, the builtin super() never works correctly for classmethods, whether the "classmethod core dump" is fixed or not. |
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msg9998 - (view) | Author: PJ Eby (pje) * ![]() |
Date: 2002-03-27 13:38 | |
Logged In: YES user_id=56214 Ugh. I just realized that my "presumable fix" is actually wrong. I checked back on my "Python super" workaround, and realized I modified Guido's example slightly, to call __get__(self.__obj__,starttype), instead of __get__(self.__obj__). This implies that the fix to super_getattro is a little more complicated, since super_getattro doesn't have a C variable equivalent to starttype in the Python version of super. :( |
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msg9999 - (view) | Author: Michael Hudson (mwh) ![]() |
Date: 2002-03-31 20:19 | |
Logged In: YES user_id=6656 Unless someone can come up with a obviously correct patch (and convince Guido that it's obviously correct) very soon, this isn't going to go into 2.2.1. |
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msg10000 - (view) | Author: PJ Eby (pje) * ![]() |
Date: 2002-03-31 23:17 | |
Logged In: YES user_id=56214 Patch #537536 submitted to fix this. "make test" output is same as before the patch. If someone can give me an idea of where/how to insert a regression test for the bug being fixed, I'll submit a patch for that, too. Thanks. |
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msg10001 - (view) | Author: Michael Hudson (mwh) ![]() |
Date: 2002-04-01 09:36 | |
Logged In: YES user_id=6656 Assign to Guido. Bearing in mind that I haven't even tried to understand this bug, the fact that you can't come up with a test case stands against you... if you're just asking where to put it, stick it in test_descr. |
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msg10002 - (view) | Author: PJ Eby (pje) * ![]() |
Date: 2002-04-01 19:46 | |
Logged In: YES user_id=56214 I was indeed just asking where to put it, and how to *insert* the test. Anyway, I found that most of what was needed for the test was already in test_descr.classmethods(), there were just a few conditions using super() that needed adding. I've uploaded the patch for test_descr to the patch #537536 for this bug. By the way, the bug/patch submission guidelines were a little unclear to me; specifically whether I was supposed to put the patch with the bug or the bug with the patch or upload everything to both or what. Hope my ignorance hasn't inconvenienced anyone; this is my first time submitting Python bugs and fixes. Also, I hadn't worked with the test framework used in Python's test suite before, although I've done quite a bit with unittest in my own code. |
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msg10003 - (view) | Author: Michael Hudson (mwh) ![]() |
Date: 2002-04-01 20:50 | |
Logged In: YES user_id=6656 OK, you've found the right place, good. The bug/patch guidlines are probably confusing because, unless you're part of the Python project I think you can't attach a file to a report you didn't submit. Generally I prefer patches to be attached to bugs, but that's just my opinion, I don't know what other developers think. I also think the whole bug/patch division is misguided, but that's another rant entirely. I think you're doing fine! Now we just wait for Guido to stop changing nappies :) |
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msg10004 - (view) | Author: Guido van Rossum (gvanrossum) * ![]() |
Date: 2002-04-02 21:27 | |
Logged In: YES user_id=6380 I should probably mention that I checked in Phillip's patch 537536, closing this issue. |
History | |||
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Date | User | Action | Args |
2022-04-10 16:05:09 | admin | set | github: 36335 |
2002-03-26 22:13:29 | pje | create |