Christopher Smith added the comment:
On Sun, Oct 6, 2013 at 12:14 AM, Raymond Hettinger
<[email protected]>wrote:
>
> Raymond Hettinger added the comment:
>
> Christopher, this tracker item needs to die. It is wasting everyone's
> time (and churning code) over nothing.
>
>
but it's not quite dead yet...
> FYI, I moved the _int=int for shuffle inside the function because the
> assignment was outside of the inner loop, so we weren't getting any real
> benefit.
>
but cf Tim's comment regarding the advantage of leaving it in the arg list
so that the lookup is fast:
[Senthil Kumaran]
> I am unaware of the optimization technique you refer to as
> well, it will helpful if you could point to any resource.
It's an old trick since the very first Pythons: global lookups are
much slower than local lookups (the difference between the LOAD_GLOBAL
and LOAD_FAST opcodes in CPython). Putting:
..., _fast=slow, ...
in an argument list means we endure the slow lookup (of `slow`) only
once, when the function is first defined. When the function is
_called_, that binding is available via the local (much faster lookup)
variable `_fast`.
Purely a speed trick, but can make a real difference in very heavily
used functions.
----------
So by removing it from the arg list you have perhaps caused a regression in
performance of shuffle. Other than that, everything looks fine to me.
Thanks,
Chris
----------
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<http://bugs.python.org/issue14927>
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