[Python-Dev] Please reject or postpone PEP 526

[Koos Zevenhoven]

On Mon, Sep 5, 2016 at 1:04 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 5 September 2016 at 18:19, Koos Zevenhoven <k7hoven at gmail.com> wrote:
>> On Mon, Sep 5, 2016 at 5:21 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>>> On 5 September 2016 at 04:40, Koos Zevenhoven <k7hoven at gmail.com> wrote:
>>>> On Sun, Sep 4, 2016 at 9:13 PM, Ivan Levkivskyi <levkivskyi at gmail.com> wrote:
>>>>> On 4 September 2016 at 19:59, Nick Coghlan <ncoghlan at gmail.com> wrote:
>>>> [...]
>>>>>>
>>>>>> Similarly, it would be reasonable to say that these three snippets
>>>>>> should all be equivalent from a typechecking perspective:
>>>>>>
>>>>>>     x = None # type: Optional[T]
>>>>>>
>>>>>>     x: Optional[T] = None
>>>>>>
>>>>>>     x: Optional[T]
>>>>>>     x = None
>>>>>
>>>>>
>>>>> Nice idea, explicit is better than implicit.
>>>>
>>>> How is it going to help that these are equivalent within one checker,
>>>> if the meaning may differ across checkers?
>>>
>>> For typechecker developers, it provides absolute clarity that the
>>> semantics of the new annotations should match the behaviour of
>>> existing type comments when there's an initialiser present,
>>
>> I understood that, but what's the benefit? I hope there will be a type
>> checker that breaks this "rule".
>
> Such a typechecker means you're not writing Python anymore, you're
> writing Java/C++/C# in a language that isn't designed to be used that
> way.

I'm glad those are all the languages you accuse me of. The list could
have been a lot worse. I actually have some good memories of Java. It
felt kind of cool at that age, and it taught me many things about
undertanding the structure of large and complicated programs after I
had been programming for years in other languages, including C++. It
also taught me to value simplicity instead, so here we are.

> Fortunately, none of the current typecheckers have made that mistake,
> nor does anyone appear to be promoting this mindset outside this
> particular discussion.

The thing I'm promoting here is to not add anything to PEP 526 that
says what a type checker is supposed to do with type annotations.
Quite the opposite of Java/C++/C#, I would say.

We can, of course, speculate about the future of type checkers and the
implications of PEP 526 on it. That's what I'm trying to do on
python-ideas, speculate about the best kind of type checking
(achievable with PEP 526 annotations) [1].

--Koos


[1] https://mail.python.org/pipermail/python-ideas/2016-September/042076.html

>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia



-- 
+ Koos Zevenhoven + http://twitter.com/k7hoven +