[Python-ideas] PEP 550 v2

[Nick Coghlan]

On 21 August 2017 at 07:01, Barry <barry at barrys-emacs.org> wrote:
> I'm not clear why there is a new_context_key which seems not to be a key.
> It seems that the object is a container for a single value.
>
> Key.set( value ) does not feel right.

It's basically borrowed from procedural thread local APIs, which tend
to use APIs like "tss_set(key, value)".

That said, in a separate discussion, Caleb Hattingh mentioned C#'s
AsyncLocal API, and it occurred to me that "context local" might work
well as the name of the context access API:

    my_implicit_state = sys.new_context_local('my_state')
    my_implicit_state.set('spam')

    # Later, to access the value of my_implicit_state:
    print(my_implicit_state.get())

That way, we'd have 3 clearly defined kinds of local variables:

* frame locals (the regular kind)
* thread locals (threading.locals() et al)
* context locals (PEP 550)

The fact contexts can be nested, and a failed lookup in the active
implicit context may then query outer namespaces in the current
execution context would then be directly analogous to the way name
lookups are resolved for frame locals.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia