[Twisted-Python] How to get the class of the wrapped fget/fset property methods

[Adi Roiban]

On 23 November 2015 at 02:32, Glyph Lefkowitz <glyph at twistedmatrix.com>
wrote:

>
> On Nov 22, 2015, at 07:04, Adi Roiban <adi at roiban.ro> wrote:
>
> The @deprecated decorator (at leas on py2.7) does not work when paired
> @property
>
> For deprecated instance variables, our deprecation policy recommend
> converting them into properties and emitted the  warning from there.
> It would be nice if we could use the standard @deprecated decorator here.
>
> The problem is that when property are used the fget/fset are received by
> the @deprecated wrapper as functions and not as methods
>
> Is there a way to get the class in which a property is defined... or there
> is no way to use the @deprecated decorator with the @property .. and we
> should create a dedicated deprecatedMember method which is called as a
> normal method.
>
>
> If you care about inheritance, the implementation is a little bit tricky,
> because you have to manually walk the class hierarchy looking for the
> attribute.  But conceptually it's pretty simple: just look at the type of
> 'oself' in the __get__ method of the returned descriptor.
>
> Right now, @deprecated is hard-coded to assume a function, but it could be
> repurposed to work with specific other descriptor types reasonably easily.
> *Arbitrary* descriptors might be hard, because it's not clear when to
> emit the message, but specific types like @property should be pretty
> straightforward with an instance check.
>
> I think that we can go with a dedicated instance check for properties...
this is about the @deprecated decorator and using it together with the
deprecation policy for instance members.

I have created a dedicated ticket https://twistedmatrix.com/trac/ticket/8124


I still don't know how to fix it... I tried following property.__get__ and
property.getter and property.fget

>From what I understand of how Python works, at the time when the decorator
is called, the class is not yet created  / does not yet exists.

This will not work

class SomeClass(object):

    @deprecated(
        Version("Twisted", 16, 0, 0), 'the deferred returned by start()')
    @property
    def deferred(self):
        """
        DEPRECATED. Deferred fired when loop stops or fails.
        """
        return self._deferred

And I should use something like this

class SomeClass(object):

    @property
    def deferred(self):
        """
        DEPRECATED. Deferred fired when loop stops or fails.
        """
        deprecated(
            Version("Twisted", 16, 0, 0), 'the deferred returned by
start()')
        return self._deferred

---------


Will push the tests and will ask for help in the review queue.

Thanks!

-- 
Adi Roiban
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