[Python-Dev] Making proxy types easier to write and maintain

[Nick Coghlan]

On 20 Mar 2014 06:24, "Antoine Pitrou" <solipsis at pitrou.net> wrote:
>
> On Wed, 19 Mar 2014 19:32:50 +0000
> Brett Cannon <bcannon at gmail.com> wrote:
> > >
> > > In http://bugs.python.org/issue19359#msg213530 I proposed to
introduce a
> > > "proxy
> > > protocol" (__proxy__ / tp_proxy) that would be used as a fallback by
> > > _PyObject_LookupSpecial to fetch the lookup target, i.e.:
> > >
> > > def _PyObject_LookupSpecial(obj, name):
> > >     tp = type(obj)
> > >     try:
> > >         return getattr(tp, name)
> > >     except AttributeError:
> > >         return getattr(tp.tp_proxy(), name)
> > >
> > > What do you think?
> > >
> >
> >  Without having the code in front of me, would this only be for magic
> > methods and attributes, or all attributes? IOW would this mean that if I
> > assign an object to __proxy__ it would take care of the uses of
__getattr__
> > for proxying?
>
> In a first approach it would be only for magic methods and attributes.
> It if proves successful, perhaps it can be later expanded to also be
> used for regular lookups.
>
> By the way, Benjamin pointed me to a prior discussion:
> http://bugs.python.org/issue643841

Graeme Dumpleton has also subsequently written a library to handle easier
creation of correct proxy types: https://pypi.python.org/pypi/wrapt

It isn't as simple as changing one lookup function though - abstract.c
reads the type slots directly, and those are already hairy performance
critical code paths (especially the binary operator type dispatch).

Cheers,
Nick.

>
> Regards
>
> Antoine.
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