[Python-Dev] PEP 549: Instance Properties (aka: module properties)
larry at hastings.org
Mon Sep 11 21:04:33 EDT 2017
On 09/11/2017 08:44 AM, Guido van Rossum wrote:
> I worry that in the end @property isn't general enough and the major
> use cases end up still having to use __class__ assignment, and then
> we'd have a fairly useless feature that we cant withdraw, ever.
What can I say--I don't have that worry ;-)
As previously mentioned in this thread, I counted up uses of property,
__getattr__, and __getattribute__ in 3.7/Lib. I grepped for the
following strings, ignored pydoc_data/topics.py, and got these totals:
"@property" 375 hits
"def __getattr__" 28 hits
"def __getattribute__(" 2 hits
@property seems pretty popular.
>> Why is there no mechanism to add new descriptors that can work in
>> this context?
> I've updated the prototype to add one. I added it as
> "collections.abc.InstanceDescriptor"; that's a base class you can
> inherit from, and then your descriptor will work in a module.
> Bikeshedding the name is fine.
> I don't understand the question, or the answer. (And finding the
> prototype is taking longer than writing this email.)
Ronald was basically asking: what about user classes? The first
revision of the prototype didn't provide a way to write your own
instance descriptors. The only thing that could be a instance
descriptor was property. So, I updated the prototype and added
collections.abc.InstanceDescriptor, a base class user classes can
inherit from that lets them be instance descriptors.
The prototype is linked to from the PEP; for your convenience here's a link:
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