Message 199032 - Python tracker (original) (raw)

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