[Python-Dev] Lukewarm about range literals

[Tim Peters]

[Skip Montanaro]
> One of the original arguments for range literals as I recall was that
> indexing of loops could get more efficient.  The compiler would know
> that [0:100:2] represents a series of integers and could conceivably
> generate more efficient loop indexing code (and so could Python2C and
> other compilers that generated C code).  This argument doesn't seem to
> be showing up here at all.  Does it carry no weight in the face of the
> relative inscrutability of the syntax?

It carries no weight at all *for 2.0* because the patch didn't exploit the
efficiency possibilities.

Which I expect are highly overrated (maybe 3% in a "good case" real-life
loop) anyway.  Even if they aren't, the same argument would apply to any
other new syntax for this too, so in no case is it an argument in favor of
this specific new syntax over alternative new syntaxes.

There are also well-known ways to optimize the current "range" exactly the
way Python works today; e.g., compile two versions of the loop, one assuming
range is the builtin, the other assuming it may be anything, then a quick
runtime test to jump to the right one.  Guido hates that idea just because
it's despicable <wink>, but that's the kind of stuff optimizing compilers
*do*, and if we're going to get excited about efficiency then we need to
consider *all sorts of* despicable tricks like that.

In any case, I've spent 5 hours straight now digging thru Python email, have
more backed up than when I started, and have gotten nothing done today
toward moving 2.0b1 along.  I'd love to talk more about all this, but there
simply isn't the time for it now ...