[Python-Dev] PEP 550 v3 (original) (raw)

Koos Zevenhoven k7hoven at gmail.com
Tue Aug 22 02:06:35 EDT 2017

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.

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