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Tue Aug 22 02:06:35 EDT 2017 · https://mail.python.org/pipermail/python-dev/2017-August/148886.html

On Tue, Aug 22, 2017 at 12:44 AM, Yury Selivanov <yselivanov.ml at gmail.com>
wrote:

> On Mon, Aug 21, 2017 at 5:39 PM, Koos Zevenhoven <k7hoven at gmail.com>
> wrote:
> [..]
> >> In the current version of the PEP, generators are initialized with an
> >> empty LogicalContext.  When they are being iterated (started or
> >> resumed), their LogicalContext is pushed to the EC.  When the
> >> iteration is stopped (or paused), they pop their LC from the EC.
> >>
> >
> > Another quick one before I go: Do we really need to push and pop a LC on
> > each next() call, even if it most likely will never be touched?
>
> Yes, otherwise it will be hard to maintain the consistency of the stack.
>
> There will be an optimization: if the LC is empty, we will push NULL
> to the stack, thus avoiding the cost of allocating an object.
>
> 
But if LCs are immutable, there needs to be only one empty-LC instance.
That would avoid special-casing NULL in code.

-- Koos

> I measured the overhead -- generators will become 0.5-1% slower in
> microbenchmarks, but only when they do pretty much nothing. If a
> generator contains more Python code than a bare "yield" expression,
> the overhead will be harder to detect.

-- 
+ Koos Zevenhoven + http://twitter.com/k7hoven +
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[Python-Dev] PEP 550 v3