[New-bugs-announce] [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 at python
components: Documentation, Interpreter Core
messages: 173183
nosy: christopherthemagnificent, docs at 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

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16267>
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