[Python-ideas] PEP 550 v2

[Nick Coghlan]

On 17 August 2017 at 00:25, Stefan Krah <stefan at bytereef.org> wrote:
> Perhaps it would be possible to name the data structures by their functionality.
> E.g. if ExecutionContext is a stack, use ExecutionStack?
>
> Or if the dynamic scope angle should be highlighted, perhaps ExecutionScope
> or even DynamicScope.
>
> This sounds like bikeshedding, but I find it difficult to have ExecutionContext,
> ContextItem, LocalContext in addition to the actual decimal.localcontext()
> and PyDecContext.
>
> For example, should PyDecContext inherit from ContextItem?  I don't fully
> understand. :-/

Agreed, I don't think we have the terminology quite right yet.

For "ContextItem" for example, we may actually be better off calling
it "ContextKey", and have the methods be "ck.get_value()" and
"ck.set_value()". That would get us closer to the POSIX TSS
terminology, and emphasises that the objects themselves are best seen
as opaque references to a key that lets you get and set the
corresponding value in the active execution context.

I do think we should stick with "context" rather than bringing dynamic
scopes into the mix - while dynamic scoping *is* an accurate term for
what we're doing at a computer science level, Python itself tends to
reserve the term scoping for the way the compiler resolves names,
which we're deliberately *not* touching here.

Avoiding a naming collision with decimal.localcontext() would also be desirable.

Yury, what do you think about moving the ExecutionContext name to what
the PEP currently calls LocalContext, and renaming the current
ExecutionContext type to ExecutionContextChain?

The latter name then hints at the collections.ChainMap style behaviour
of ck.get_value() lookups, without making any particular claims about
what the internal implementation data structures actually are.

The run methods could then be sys.run_with_context_chain() (to ignore
the current context entirely and use a completely separate context
chain) and sys.run_with_active_context() (to append a single execution
context onto the end of the current context chain)

Cheers,
Nick.

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