[Python-Dev] Scope, not context? (was Re: PEP 550 v3 naming) (original) (raw)

Eric Snow ericsnowcurrently at gmail.com
Fri Aug 25 11:15:03 EDT 2017

On Fri, Aug 25, 2017 at 8:18 AM, Yury Selivanov <yselivanov.ml at gmail.com> wrote:

Another idea:

1. We alter PyModule to make it possible to add properties (descriptor protocol, or we implement custom getattr). I think we can make it so that only sys module would be able to actually use it, so it's not going to be a new feature -- just a hack for CPython.

FWIW, I've been toying with a similar problem and solution for a while. I'd like to clean up the sys module, including grouping some of the attributes (e.g. the import state), turn the get/set pairs into properties, and deprecate direct usage of some of the attributes.

Though supporting descriptors on module objects would work [1] and be useful (particularly deprecating module attrs), it's sufficiently worthy of a PEP that I haven't taken the time. Instead, the approach I settled on was to rename sys to _sys and add a sys written in Python that proxies _sys. Here's a rough first pass:

https://github.com/ericsnowcurrently/cpython/tree/sys-module

It's effectively the same thing as ModuleType supporting descriptors, but specific only to sys. One problem with both approaches is that we'd be changing the type of the sys module. There's a relatively common idiom in the stdlib (and elsewhere) of using "type(sys)" to get ModuleType. Changing the type of the sys module breaks that.

-eric

[1] This is doable with a custom getattribute on ModuleType, though it will impact attribute lookup on all modules. I suppose there could be a subclass that does the right thing... Anyway, this is more python-ideas territory.

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