Author smichr
Recipients eric.araujo, ezio.melotti, georg.brandl, michael.driscoll, orsenthil, python-dev, rhettinger, sandro.tosi, smichr, tim.peters
Date 2013-10-06.06:44:45
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In-reply-to <1381036484.68.0.505839833504.issue14927@psf.upfronthosting.co.za>
Content
On Sun, Oct 6, 2013 at 12:14 AM, Raymond Hettinger
<report@bugs.python.org>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
History
Date User Action Args
2013-10-06 06:44:45smichrsetrecipients: + smichr, tim.peters, georg.brandl, rhettinger, orsenthil, ezio.melotti, eric.araujo, sandro.tosi, python-dev, michael.driscoll
2013-10-06 06:44:45smichrlinkissue14927 messages
2013-10-06 06:44:45smichrcreate