[Python-Dev] PEP487: Simpler customization of class creation

[Eric Snow]

Great job, Martin!  Thanks for seeing this through. :)

-eric

On Sun, Jul 17, 2016 at 10:57 AM, Guido van Rossum <guido at python.org> wrote:
> This PEP is now accepted for inclusion in Python 3.6. Martin,
> congratulations! Someone (not me) needs to review and commit your
> changes, before September 12, when the 3.6 feature freeze goes into
> effect (see https://www.python.org/dev/peps/pep-0494/#schedule).
>
> On Sun, Jul 17, 2016 at 4:32 AM, Martin Teichmann
> <lkb.teichmann at gmail.com> wrote:
>> Hi Guido, Hi Nick, Hi list,
>>
>> so I just updated PEP 487, you can find it here:
>> https://github.com/python/peps/pull/57 if it hasn't already been
>> merged. There are no substantial updates there, I only updated the
>> wording as suggested, and added some words about backwards
>> compatibility as hinted by Nick.
>>
>> Greetings
>>
>> Martin
>>
>> 2016-07-14 17:47 GMT+02:00 Guido van Rossum <guido at python.org>:
>>> I just reviewed the changes you made, I like __set_name__(). I'll just
>>> wait for your next update, incorporating Nick's suggestions. Regarding
>>> who merges PRs to the PEPs repo, since you are the author the people
>>> who merge don't pass any judgment on the changes (unless it doesn't
>>> build cleanly or maybe if they see a typo). If you intend a PR as a
>>> base for discussion you can add a comment saying e.g. "Don't merge
>>> yet". If you call out @gvanrossum, GitHub will make sure I get a
>>> message about it.
>>>
>>> I think the substantial discussion about the PEP should remain here in
>>> python-dev; comments about typos, grammar and other minor editorial
>>> issues can go on GitHub. Hope this part of the process makes sense!
>>>
>>> On Thu, Jul 14, 2016 at 6:50 AM, Martin Teichmann
>>> <lkb.teichmann at gmail.com> wrote:
>>>> Hi Guido, Hi list,
>>>>
>>>> Thanks for the nice review! I applied followed up your ideas and put
>>>> it into a github pull request: https://github.com/python/peps/pull/53
>>>>
>>>> Soon we'll be working there, until then, some responses to your comments:
>>>>
>>>>> I wonder if this should be renamed to __set_name__ or something else
>>>>> that clarifies we're passing it the name of the attribute? The method
>>>>> name __set_owner__ made me assume this is about the owning object
>>>>> (which is often a useful term in other discussions about objects),
>>>>> whereas it is really about telling the descriptor the name of the
>>>>> attribute for which it applies.
>>>>
>>>> The name for this has been discussed a bit already, __set_owner__ was
>>>> Nick's idea, and indeed, the owner is also set. Technically,
>>>> __set_owner_and_name__ would be correct, but actually I like your idea
>>>> of __set_name__.
>>>>
>>>>> That (inheriting type from type, and object from object) is very
>>>>> confusing. Why not just define new classes e.g. NewType and NewObject
>>>>> here, since it's just pseudo code anyway?
>>>>
>>>> Actually, it's real code. If you drop those lines at the beginning of
>>>> the tests for the implementation (as I have done here:
>>>> https://github.com/tecki/cpython/blob/pep487b/Lib/test/test_subclassinit.py),
>>>> the test runs on older Pythons.
>>>>
>>>> But I see that my idea to formulate things here in Python was a bad
>>>> idea, I will put the explanation first and turn the code into
>>>> pseudo-code.
>>>>
>>>>>>         def __init__(self, name, bases, ns, **kwargs):
>>>>>>             super().__init__(name, bases, ns)
>>>>>
>>>>> What does this definition of __init__ add?
>>>>
>>>> It removes the keyword arguments. I describe that in prose a bit down.
>>>>
>>>>>>     class object:
>>>>>>         @classmethod
>>>>>>         def __init_subclass__(cls):
>>>>>>             pass
>>>>>>
>>>>>>     class object(object, metaclass=type):
>>>>>>         pass
>>>>>
>>>>> Eek! Too many things named object.
>>>>
>>>> Well, I had to do that to make the tests run... I'll take that out.
>>>>
>>>>>> In the new code, it is not ``__init__`` that complains about keyword arguments,
>>>>>> but ``__init_subclass__``, whose default implementation takes no arguments. In
>>>>>> a classical inheritance scheme using the method resolution order, each
>>>>>> ``__init_subclass__`` may take out it's keyword arguments until none are left,
>>>>>> which is checked by the default implementation of ``__init_subclass__``.
>>>>>
>>>>> I called this out previously, and I am still a bit uncomfortable with
>>>>> the backwards incompatibility here. But I believe what you describe
>>>>> here is the compromise proposed by Nick, and if that's the case I have
>>>>> peace with it.
>>>>
>>>> No, this is not Nick's compromise, this is my original. Nick just sent
>>>> another mail to this list where he goes a bit more into the details,
>>>> I'll respond to that about this topic.
>>>>
>>>> Greetings
>>>>
>>>> Martin
>>>>
>>>> P.S.: I just realized that my changes to the PEP were accepted by
>>>> someone else than Guido. I am a bit surprised about that, but I guess
>>>> this is how it works?
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>>>
>>>
>>>
>>> --
>>> --Guido van Rossum (python.org/~guido)
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>
>
> --
> --Guido van Rossum (python.org/~guido)
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