[Python-Dev] advice needed: best approach to enabling "metamodules"?

[Nathaniel Smith]

On Sun, Nov 30, 2014 at 7:27 PM, Ethan Furman <ethan at stoneleaf.us> wrote:
> On 11/30/2014 11:15 AM, Guido van Rossum wrote:
>> On Sun, Nov 30, 2014 at 6:15 AM, Brett Cannon wrote:
>>> On Sat, Nov 29, 2014, 21:55 Guido van Rossum wrote:
>>>>
>>>> All the use cases seem to be about adding some kind of getattr hook
>>>> to modules. They all seem to involve modifying the CPython C code
>>>> anyway. So why not tackle that problem head-on and modify module_getattro()
>>>> to look for a global named __getattr__ and if it exists, call that instead
>>>> of raising AttributeError?
>>>
>>> Not sure if anyone thought of it. :) Seems like a reasonable solution to me.
>>> Be curious to know what the benchmark suite said the impact was.
>>
>> Why would there be any impact? The __getattr__ hook would be similar to the
>> one on classes -- it's only invoked at the point where otherwise AttributeError
>> would be raised.
>
> I think the bigger question is how do we support it back on 2.7?

I think that's doable -- assuming I'm remembering correctly the
slightly weird class vs. instance lookup rules for special methods,
you can write a module subclass like

class GetAttrModule(types.ModuleType):
    def __getattr__(self, name):
        return self.__dict__["__getattr__"](name)

and then use ctypes hacks to get it into sys.modules[__name__].

-n

-- 
Nathaniel J. Smith
Postdoctoral researcher - Informatics - University of Edinburgh
http://vorpus.org