[Python-Dev] PEP 549 v2: now titled Instance Descriptors (original) (raw)

Ethan Furman ethan at stoneleaf.us
Fri Sep 8 16:45:13 EDT 2017

On 09/08/2017 12:44 PM, Larry Hastings wrote:

I've updated PEP 549 with a new title--"Instance Descriptors" is a better name than "Instance Properties"--and to clarify my rationale for the PEP. I've also updated the prototype with code cleanups and a new type: "collections.abc.InstanceDescriptor", a base class that allows user classes to be instance descriptors.

I like the new title, I'm +0 on the PEP itself, and I have one correction for the PEP: we've had the ability to simulate module properties for ages:

 Python 2.7.6 (default, Oct 26 2016, 20:32:47)
 [GCC 4.8.4] on linux2
 Type "help", "copyright", "credits" or "license" for more information.
 --> import module_class
 --> module_class.hello
 'hello'
 --> module_class.hello = 'hola'
 --> module_class.hello
 'hola'

And the code:

 class ModuleClass(object):
     @property
     def hello(self):
         try:
             return self._greeting
         except AttributeError:
             return 'hello'
     @hello.setter
     def hello(self, value):
         self._greeting = value

 import sys
 sys.modules[__name__] = ModuleClass()

I will admit I don't see what reassigning the class attribute on a module did for us.

-- Ethan

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