[Python-ideas] PEP 560 (second post)

Koos Zevenhoven k7hoven at gmail.com
Fri Nov 10 15:19:00 EST 2017

On Fri, Nov 10, 2017 at 8:33 PM, Ivan Levkivskyi <levkivskyi at gmail.com>

> On 10 November 2017 at 18:39, Koos Zevenhoven <k7hoven at gmail.com> wrote:
>> On Wed, Sep 27, 2017 at 12:28 PM, Ivan Levkivskyi <levkivskyi at gmail.com>
>> wrote:
>>>>> After creating the class,
>>> the original bases are saved in ``__orig_bases__`` (currently this is
>>> also
>>> done by the metaclass).
>> ​Those are *still* bases, right, even if they are not in the mro?​ I'm
>> not sure if this is a naming thing or something even more.
> The objects that have __subclass_base__ method (proposed to rename to
> __mro_entry__)
> are removed from __bases__ attributed of the newly created class.
> Otherwise they may cause a metaclass conflict.
> One can however still call them syntactic (or static?) bases. For example
> this is how it is going to be used by typing:
>     from typing import List
>     class Tokens(List[int]):
>         ...
>     assert Tokens.__bases__ == (list,)

​Why is List[int] not allowed to be the base? Neither method-lookup
performance nor the metaclass conflict issue seem to depend on whether
List[int] is in __bases__.

>> NOTE: These two method names are reserved for exclusive use by
>>> the ``typing`` module and the generic types machinery, and any other use
>>> is
>>> strongly discouraged.
>> ​Given the situation, that may be a good thing. But will it really work?
>> I think it is also strongly discouraged to invent your own dunder method
>> names, but people still do it.​
> Terry had a similar comment. I will "soften" this formulation in the next
> revision of the PEP.
Right, I assume you mean the one where he pointed out that implicitly
turning the methods into staticmethods based on their names makes those
names reserved words.
​-- Koos

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