[Python-Dev] PEP520 and absence of __definition_order__

[Nick Coghlan]

On 10 September 2016 at 17:49, Ethan Furman <ethan at stoneleaf.us> wrote:
> Per Victor's advice I'm posting this here.
>
> PEP 520 has been accepted, but without the __definition_order__ attribute.
> The accompanying comment:
>
>> "Note: Since compact dict has landed in 3.6, __definition_order__ has
>> been removed. cls.__dict__ now mostly accomplishes the same thing
>> instead."
>
>
> The "mostly" is what concerns me.  Much like having a custom __dir__ lets
> a class fine-tune what is of interest, a custom __definition_order__ allows
> a class to present a unified view of the class creation process.  This could
> be important to classes that employ __getattr__ (or __getattribute__) to
> provide virtual attributes, such as Enum or proxy classes.

+1

The reasoning for modifying the PEP post-acceptance is faulty -
__definition_order__ wasn't just there as a CPython implementation
detail, it was there as a way to allow class and metaclass developers
to hide their *own* irrelevant implementation details.

Since __definition_order__ was already accepted, and the rationale for
removing it is incorrect, could we please have it back for beta 1?

Regards,
Nick.

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