[Python-Dev] PEP 560: bases classes / confusion

[Ivan Levkivskyi]

Nick is exactly right here. Jim, if you want to propose alternative
wording, then we could consider it.

--
Ivan


On 15 November 2017 at 16:37, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 16 November 2017 at 00:20, Jim J. Jewett <jimjjewett at gmail.com> wrote:
>
>> I *think* the following will happen:
>>
>>     "NewList[int]" will be evaluated, and __class_getitem__ called, so
>> that the bases tuple will be (A, GenericAlias(NewList, int), B)
>>
>>     # (A)  I *think* __mro_entries__ gets called with the full tuple,
>>     # instead of just the object it is found on.
>>     # (B) I *think* it is called on the results of evaluating
>>     # the terms within the tuple, instead of the original
>>     # string representation.
>>     _tmp = __mro_entries__(A, GenericAlias(NewList, int), B)
>>
>>     # (C)  I *think* __mro_entries__ returns a replacement for
>>     # just the single object, even though it was called on
>>     # the whole tuple, without knowing which object it
>>     # represents.
>>     bases = (A, _tmp, B)
>>
>
> My understanding of the method signature:
>
>     def __mro_entries__(self, orig_bases):
>         ...
>         return replacement_for_self
>
> My assumption as to the purpose of the extra complexity was:
>
> - given orig_bases, a method could avoid injecting bases already listed if
> it wanted to
> - allowing multiple items to be returned provides a way to
> programmatically combine mixins without having to define a new subclass for
> each combination
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>
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