On Thu, 14 Sep 2017 at 12:09 Ivan Levkivskyi <levkivs...@gmail.com> wrote:
> On 14 September 2017 at 01:13, Guido van Rossum <gu...@python.org> wrote:
>
>>
>> That last sentence is a key observation. Do we even know whether there
>> are (non-toy) things that you can do *in principle* with __class__
>> assignment but which are too slow *in practice* to bother? And if yes, is
>> __getattr__ fast enough? @property?
>>
>>
> I myself have never implemented deprecation warnings management nor lazy
> loading,
> so it is hard to say if __class__ assignment is fast enough.
>
For lazy loading it is, but that's because after the lazy load,
module.__class__ is set back to its original value, so any performance
penalty is paid only once upon triggering __getattribute__ on the lazy
module.
IOW no one has complained and I know plenty of places using the lazy
loading mechanism in importlib at scale. :)
-Brett
> For me it is more combination
> of three factors:
>
> * modest performance improvement
> * some people might find __getattr__ clearer than __class__ assignment
> * this would be consistent with how stubs work
>
>
>> IMO we're still looking for applications.
>>
>>
> How about this
>
> def allow_forward_references(*allowed):
> caller_globals = sys._getframe().__globals__
> def typing_getattr(name):
> if name in allowed:
> return name
> raise AttributeError(...)
> caller_globals.__getattr__ = typing_getattr
>
> from typing_extensions import allow_forward_references
> allow_forward_references('Vertex', 'Edge')
>
> T = TypeVar('T', bound=Edge)
>
> class Vertex(List[Edge]):
> def copy(self: T) -> T:
> ...
>
> class Edge:
> ends: Tuple[Vertex, Vertex]
> ...
>
> Look mum, no quotes! :-)
>
> --
> Ivan
>
>
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