[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Roundup Robot]

Roundup Robot added the comment:

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

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Nick Coghlan]

Changes by Nick Coghlan ncogh...@gmail.com:


--
resolution:  - fixed
stage: needs patch - committed/rejected
status: open - closed

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Andrew Svetlov]

Andrew Svetlov added the comment:

After trying to make patch I've realized — better to leave current behavior as 
is and change documentation only.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Nick Coghlan]

Nick Coghlan added the comment:

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).

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Eric Snow]

Eric Snow added the comment:

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.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Darren Dale]

Darren Dale added the comment:

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.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Christopher the Magnificent]

New submission from Christopher the Magnificent:

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.  :-)

--
assignee: docs@python
components: Documentation, Interpreter Core
messages: 173183
nosy: christopherthemagnificent, docs@python
priority: normal
severity: normal
status: open
title: order of decorators @abstractmethod and @classmethod is significant (is 
not documented to be in @abstractclassmethod which advises their combined use)
type: behavior
versions: Python 3.3

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Andrew Svetlov]

Changes by Andrew Svetlov andrew.svet...@gmail.com:


--
nosy: +asvetlov

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Andrew Svetlov]

Andrew Svetlov added the comment:

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.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Arfrever Frehtes Taifersar Arahesis]

Changes by Arfrever Frehtes Taifersar Arahesis arfrever@gmail.com:


--
nosy: +Arfrever

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[R. David Murray]

R. David Murray added the comment:

I've added the nosy list from issue 11610, in case complicating the 
implementation is seen as sub-optimal :)

--
nosy: +Darren.Dale, benjamin.peterson, daniel.urban, dsdale24, eric.araujo, 
eric.snow, ncoghlan, python-dev, r.david.murray, stutzbach

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Benjamin Peterson]

Benjamin Peterson added the comment:

I don't see why classmethod/staticmethod should be special cased if it doesn't 
work for other decorators.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Darren Dale]

Darren Dale added the comment:

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.

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Christopher the Magnificent]

Christopher the Magnificent added the comment:

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.

:-)

--

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue16267] order of decorators @abstractmethod and @classmethod is significant (is not documented to be in @abstractclassmethod which advises their combined use)

[Andrew Svetlov]

Andrew Svetlov added the comment:

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.

--
stage:  - needs patch
versions: +Python 3.4

___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue16267
___
___
Python-bugs-list mailing list
Unsubscribe: 
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com