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.
With __definition_order__ Enum can display the actual creation order of enum
members and methods, while relying on Enum.__dict__.keys() presents a jumbled
mess with many attributes the user never wrote, the enum members either
appearing /after/ all the methods (even if actually written before), or
entirely absent.
For example, this class:
>>> class PassBy(Enum):
... value = 1
... reference = 2
... name = 3
... object = name
... def used_by_python(self):
... return self.name == 'name'
...
shows this:
>>> PassBy.__dict__.keys()
dict_keys([
'_generate_next_value_',
'__module__',
'used_by_python',
'__doc__',
'_member_names_',
'_member_map_',
'_member_type_',
'_value2member_map_',
'reference',
'object',
'__new__',
])
Notice that two of the members are missing, and all are after the method.
If __definition_order__ existed it would be this:
>>> PassBy.__definition_order__
['value', 'reference', 'name', 'object', 'used_by_python']
Which is a much more accurate picture of the user's class.
--
~Ethan~
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