[New-bugs-announce] [issue11610] Improving property to accept abstract methods

[Darren Dale]

New submission from Darren Dale <dsdale24 at gmail.com>:

I posted a suggestion at python-ideas that the declaration of abstract properties could be improved in such a way that they could be declared with either the long-form or decorator syntax using the built-in property and abc.abstractmethod:

{{{
class MyProperty(property):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        for f in (self.fget, self.fset, self.fdel):
            if getattr(f, '__isabstractmethod__', False):
                self.__isabstractmethod__ = True
                break

class C(metaclass=ABCMeta):
    @MyProperty
    @abstractmethod
    def x(self):
        pass
    @x.setter
    @abstractmethod
    def x(self, val):
        pass

    # this syntax would also be supported:
    #@abstractmethod
    #def getx(self):
    #    pass
    #@abstractmethod
    #def setx(self, val):
    #    pass
    #x = MyProperty(getx, setx)

class D(C):
    'D does not define a concrete setter and cannot be instantiated'
    @C.x.setter
    def x(self):
        return 1

class E(D):
    'E has a concrete getter and setter, and can be instantiated'
    @D.x.setter
    def x(self, val):
        pass
}}}

It is hopefully evident that a relatively minor extension can be made to the built-in property such that @abstractproperty would no longer be needed. I have prepared a patch, complete with documentation and unit tests, but unfortunately I have not been able to test it because I have not been able to build Python from a mercurial checkout on either Ubuntu 11.04 or OS X 10.6.6 (for reasons unrelated to the patch.) BDFL thought the idea sounded good for inclusion in Python-3.3, and requested I submit the patch here.

----------
components: Library (Lib)
files: property_with_abstractmethod.patch
keywords: patch
messages: 131436
nosy: dsdale24
priority: normal
severity: normal
status: open
title: Improving property to accept abstract methods
type: feature request
versions: Python 3.3
Added file: http://bugs.python.org/file21293/property_with_abstractmethod.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue11610>
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