[Python-Dev] Possible optimization for LOAD_FAST ?

Guido van Rossum guido at python.org
Wed Jan 5 19:35:58 CET 2011

On Wed, Jan 5, 2011 at 5:27 AM, Maciej Fijalkowski <fijall at gmail.com> wrote:
> How about not changing semantics and still making this optimization possible?
> PyPy already has CALL_LIKELY_BUILTIN which checks whether builtins has
> been altered (by keeping a flag on the module dictionary) and if not,
> loads a specific builtin on top of value stack.

I can only repeat what I said before. That's what everybody proposes,
and if you have the infrastructure, it's a fine solution.

But to me, those semantics aren't sacred, and I want to at least
explore an alternative.

Putting a hook on two dicts (the module globals and builtins.__dict__)
is a lot of work in CPython, and has the risk of slowing everything
down (just a tad, but still -- AFAIK dicts currently are not
hookable). Checking whether there's a global named 'len' is much
simpler in the current CPython compiler.

--Guido van Rossum (python.org/~guido)

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