[Python-Dev] PEP 549: Instance Properties (aka: module properties)

Guido van Rossum guido at python.org
Wed Sep 13 19:13:57 EDT 2017

On Wed, Sep 13, 2017 at 3:01 PM, Ivan Levkivskyi <levkivskyi at gmail.com>

> @Guido
> > One would have to introduce some kind of convention
> > where you can write properties with a leading _
> One doesn't even need the @property decorator in this case.
> For example:
> def __getattr__(name):
>     g = globals()
>     name = '_' + name
>     if name in g:
>         return g[name]()
>     raise AttributeError(...)
> def _attr():
>     "do something"
>     return actual_object
> One can even write a decorator that would change the name automatically
> (but this will require a call at the end of module to unbind original
> names).
> The space for play is infinite. The question is what exactly is needed.
> I would say that already basic customisation (like __getattr__) will be
> enough.
> IIUC, this will be actually a bit faster than setting __class__ since only
> "customized"
> attributes will be affected.

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?

IMO we're still looking for applications.

--Guido van Rossum (python.org/~guido)
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