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Created on 2012年10月17日 15:41 by christopherthemagnificent, last changed 2022年04月11日 14:57 by admin. This issue is now closed.
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| msg173183 - (view) | Author: Christopher the Magnificent (christopherthemagnificent) | Date: 2012年10月17日 15:41 | |
This may be an issue with the interpreter behavior or it may be a documentation issue. Note: I only selected Python 3.3 as the version, but it probably affects MANY other Python versions. Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 01:25:11) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin Type "copyright", "credits" or "license()" for more information. >>> import abc >>> help(abc.abstractclassmethod) Help on class abstractclassmethod in module abc: class abstractclassmethod(builtins.classmethod) | A decorator indicating abstract classmethods. | | Similar to abstractmethod. | | Usage: | | class C(metaclass=ABCMeta): | @abstractclassmethod | def my_abstract_classmethod(cls, ...): | ... | | 'abstractclassmethod' is deprecated. Use 'classmethod' with | 'abstractmethod' instead. . (et cetra) . . >>> # doesn't work >>> class Demo(metaclass=abc.ABCMeta): ... @abc.abstractmethod ... @classmethod ... def test(cls): ... pass ... Traceback (most recent call last): File "<pyshell#26>", line 1, in <module> class Demo3(metaclass=abc.ABCMeta): File "<pyshell#26>", line 3, in Demo3 @classmethod File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/abc.py", line 24, in abstractmethod funcobj.__isabstractmethod__ = True AttributeError: attribute '__isabstractmethod__' of 'classmethod' objects is not writable >>> # DOES work >>> class Demo2(metaclass=abc.ABCMeta): ... @classmethod ... @abc.abstractmethod ... def test(cls): ... pass ... >>> Demo2() Traceback (most recent call last): File "<pyshell#33>", line 1, in <module> Demo4() TypeError: Can't instantiate abstract class Demo2 with abstract methods test Hopefully this is enough documentation to show what the issues is. If not, just chime in. :-) |
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| msg173184 - (view) | Author: Andrew Svetlov (asvetlov) * (Python committer) | Date: 2012年10月17日 16:40 | |
I think better to fix code to make first sample also work. It can be done as special cases in abc.abstractmethod to process classmethod/staticmethod objects properly. |
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| msg173188 - (view) | Author: R. David Murray (r.david.murray) * (Python committer) | Date: 2012年10月17日 17:47 | |
I've added the nosy list from issue 11610, in case complicating the implementation is seen as sub-optimal :) |
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| msg173189 - (view) | Author: Benjamin Peterson (benjamin.peterson) * (Python committer) | Date: 2012年10月17日 18:07 | |
I don't see why classmethod/staticmethod should be special cased if it doesn't work for other decorators. |
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| msg173190 - (view) | Author: Darren Dale (dsdale24) | Date: 2012年10月17日 18:15 | |
Quoting the documentation for abstractmethod: "When abstractmethod() is applied in combination with other method descriptors, it should be applied as the innermost decorator, as shown in the following usage examples:" The examples include staticmethod and classmethod. |
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| msg173198 - (view) | Author: Christopher the Magnificent (christopherthemagnificent) | Date: 2012年10月17日 19:26 | |
As Darren Dale pointed out, it looks like this is a (partial) documentation issue. I think it's plausible that someone like me, who has used abstractmethod by itself, would read the docs for abstractclassmethod and not re-read the docs on abstract method to know that he needs to put the one decorator first and other other second. Changing Python to make it indifferent to the order of classmethod and abstractmethod wouldn't be a bad idea if it isn't too hairy to implement, since it does not seem to be intuitive to me and probably others that the order of the decorators in this specific situation should matter. At bare minimum, I recommend that the documentation for abstractclassmethod and abstractstaticmethod should be updated to indicate not merely that abstractmethod and either classmethod or staticmethod should be used together, but IN WHICH ORDER they should be used, if it is decided to preserve the sensitivity to ordering. :-) |
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| msg173200 - (view) | Author: Andrew Svetlov (asvetlov) * (Python committer) | Date: 2012年10月17日 20:00 | |
After brief looking sources I figured out it can be solved by adding setters for __isabstractmethod__ to classmethod/staticmethod objects. It can be done, I'll try to make a patch. For property situation is worse: property is abstract if any of getter/setter/deleter is abstract. Which object attribute should be set for setting __isabstractmethod__ for property? We can make the rule: abstractmethod for classmethod/staticmethod/property should set descriptor as abstract, not functions behind it. I'm not sure is it true solution but I like to try to make a patch for that. Anyway, the patch for describing current behavior in the docs is welcome. |
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| msg173280 - (view) | Author: Eric Snow (eric.snow) * (Python committer) | Date: 2012年10月18日 15:54 | |
The catch is that when abstractmethod is the inner decorator, __isabstractmethod__ is set on the object that classmethod/staticmethod is wrapping. When abstractmethod is the outer decorator, __isabstractmethod__ is set on the resulting classmethod/staticmethod object instead. Unless there is some practical reason that the distinction matters, I'm +1 on letting __isabstractmethod__ be set on classmethods and staticmethods. |
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| msg173282 - (view) | Author: Darren Dale (Darren.Dale) | Date: 2012年10月18日 16:32 | |
There is a very practical reason, which was the whole point of issue11610. Descriptors are should declare themselves abstract when they are composed of abstract methods. If you have a property with an concrete getter but an abstract setter, the property should declare itself abstract until such time as it is provided a concrete setter. If we allow __isabstractmethod__ to be settable by @abstractmethod, it undermines the whole scheme of descriptors delegating their abstractedness to the methods of which they are composed. |
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| msg175417 - (view) | Author: Alyssa Coghlan (ncoghlan) * (Python committer) | Date: 2012年11月12日 02:53 | |
It took me a while to get my brain back up to speed with the full rationale behind the current design (mostly by rereading the multitude of comment on #11610). As Darren says, the main advantage of the current scheme is that the wrapper descriptors deliberately *don't* have any concept of abstract/non-abstract independent of the methods that make them up. So I think the main thing to do is change the documentation of the affected descriptors to be more explicit about the required order of the replacement decorators. Otherwise people are likely to map "abstractXmethod" to "@abstractmethod + @Xmethod" and write them in that order (which won't work). |
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| msg176823 - (view) | Author: Andrew Svetlov (asvetlov) * (Python committer) | Date: 2012年12月03日 00:42 | |
After trying to make patch I've realized — better to leave current behavior as is and change documentation only. |
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| msg177159 - (view) | Author: Roundup Robot (python-dev) (Python triager) | Date: 2012年12月08日 12:57 | |
New changeset 3345afd6dc61 by Nick Coghlan in branch '3.3': Close issue #16267: better docs for @abstractmethod composition http://hg.python.org/cpython/rev/3345afd6dc61 New changeset be7202c38089 by Nick Coghlan in branch 'default': Merge from 3.3 (issue #16267) http://hg.python.org/cpython/rev/be7202c38089 |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022年04月11日 14:57:37 | admin | set | github: 60471 |
| 2012年12月09日 05:01:11 | ncoghlan | set | status: open -> closed resolution: fixed stage: needs patch -> resolved |
| 2012年12月08日 12:57:33 | python-dev | set | messages: + msg177159 |
| 2012年12月03日 00:42:06 | asvetlov | set | messages: + msg176823 |
| 2012年11月12日 02:53:16 | ncoghlan | set | messages: + msg175417 |
| 2012年10月18日 16:32:17 | Darren.Dale | set | messages: + msg173282 |
| 2012年10月18日 15:54:40 | eric.snow | set | messages: + msg173280 |
| 2012年10月17日 20:00:19 | asvetlov | set | stage: needs patch messages: + msg173200 versions: + Python 3.4 |
| 2012年10月17日 19:26:45 | christopherthemagnificent | set | messages: + msg173198 |
| 2012年10月17日 18:15:10 | dsdale24 | set | messages: + msg173190 |
| 2012年10月17日 18:07:00 | benjamin.peterson | set | messages: + msg173189 |
| 2012年10月17日 17:47:51 | r.david.murray | set | nosy:
+ stutzbach, dsdale24, python-dev, eric.snow, ncoghlan, daniel.urban, eric.araujo, Darren.Dale, r.david.murray, benjamin.peterson messages: + msg173188 |
| 2012年10月17日 17:02:10 | Arfrever | set | nosy:
+ Arfrever |
| 2012年10月17日 16:40:26 | asvetlov | set | messages: + msg173184 |
| 2012年10月17日 16:33:48 | asvetlov | set | nosy:
+ asvetlov |
| 2012年10月17日 15:41:20 | christopherthemagnificent | create | |