[Python-Dev] Submitting PEP 422 (Simple class initialization hook) for pronouncement

[Antoine Pitrou]

On Sun, 10 Feb 2013 16:27:49 -0500
PJ Eby <pje at telecommunity.com> wrote:
> On Sun, Feb 10, 2013 at 7:32 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> >    class Example:
> >        @classmethod
> >        def __init_class__(cls):
> 
> Is the @classmethod required?  What happens if it's not present?
> 
> Second, will type have a default __init_class__?  (IMO, it should,
> otherwise it will be impossible to write co-operative __init_class__
> functions.)
> 
> Only other comment is that the PEP could use a more concrete use case, e.g.:
> 
>     class Record:
>         __fields = {}
> 
>         @classmethod
>         def __init_class__(cls):
>              cls.__fields = dict(cls.__fields)  # inherited fields
>              cls.__fields.update({attr:val for attr, val in
> cls.__dict__.iteritems() if isinstance(val, Field)})
>              super().__init_class__()   # be co-operative
> 
>          # ...other methods that use the __fields attribute
> 
>     class SomeRecord(Record):
>           foo = Field(int)
>           bar = Field(str)
> 
> Putting something like this early on might help to demonstrate the
> usefulness of the feature on its own merits, independent of the
> porting issue, etc.  ;-)

Can you explain what the example does / is supposed to do?