ncoghlan at gmail
May 20, 2008, 7:33 AM
Views: 810
Permalink
|
|
Issue 643841: Including a new-style proxy base class in 2.6/3.0
|
|
One of the tasks where classic classes are currently far superior to
new-style classes is in writing proxy classes like weakref.proxy - cases
where nearly all operations need to be delegated to some other object,
with only a few being handled via the proxy type object itself.
With classic classes, this is trivial, since __getattr__ is always
consulted, even for retrieval of special methods.
With new-style classes, however, the __getattribute__ machinery can be
bypassed, meaning the only way to proxy an arbitrary instance is to
define all of the special methods that have C-level slots.
This issue was actually first raised five and a half years ago [1], but
has never been a particularly pressing problem, as anyone with any sense
that needed to write a proxy object just used a classic class instead of
a new-style one. In 3.0, with the demise of classic classes, that
workaround goes away.
So what do people think of including a ProxyBase implementation in 2.6
and 3.0 that explicitly delegates all of the C-level slots to a
designated target instance? For some proxy class implementers, it would
be possible to use this class as a base-class to get the special method
delegation 'for free', and for others with more esoteric needs, it would
at least provide a reference for which special methods needed to be
provided explicitly by the proxy type.
I attached a sample implementation to [1] which is essentially
equivalent to weakref.proxy, but with a strong reference to the target,
and written in Python rather than C.
I expect the target audience for such a feature to be quite small, but
without better support for it in the standard library, I also suspect it
could prove to be a show-stopper for the affected developers as far as
Py3k migration is concerned.
Cheers,
Nick.
[1] http://bugs.python.org/issue643841
--
Nick Coghlan | ncoghlan[at]gmail.com | Brisbane, Australia
---------------------------------------------------------------
http://www.boredomandlaziness.org
_______________________________________________
Python-Dev mailing list
Python-Dev[at]python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe: http://mail.python.org/mailman/options/python-dev/list-python-dev%40lists.gossamer-threads.com
|
Issue 643841: Including a new-style proxy base class in 2.6/3.0
