[Python-3000] Droping find/rfind?

Guido van Rossum guido at python.org
Fri Aug 25 19:53:15 CEST 2006

On 8/25/06, Jean-Paul Calderone <exarkun at divmod.com> wrote:
> >For the record, I think this is a major case of YAGNI. You appear way
> >to obsessed with performance of some microscopic aspect of the
> >language. Please stop firing random proposals until you actually have
> >working code and proof that it matters. Speeding up microbenchmarks is
> >irrelevant.
> Twisted's core loop uses string views to avoid unnecessary copying.  This
> has proven to be a real-world speedup.  This isn't a synthetic benchmark
> or a micro-optimization.

OK, that's the kind of data I was hoping for; if this was mentioned
before I apologize. Did they implement this in C or in Python? Can you
point us to the docs for their API?

> I don't understand the resistance.  Is it really so earth-shatteringly
> surprising that not copying memory unnecessarily is faster than copying
> memory unnecessarily?

It depends on how much bookkeeping is needed to properly free the
underlying buffer when it is no longer referenced, and whether the
application repeatedly takes short long-lived slices of long otherwise
short-lived buffers. Unless you have a heuristic for deciding to copy
at some point, you may waste a lot of space.

> If the goal is to avoid speeding up Python programs because views are too
> complex or unpythonic or whatever, fine.  But there isn't really any
> question as to whether or not this is a real optimization.

There are many ways to implement views. It has often been proposed to
make views an automatic feature of the basic string object. There the
optimization in one case has to be weighed against the pessimization
in another case (like the bookkeeping overhead everywhere and the
worst-case scenario I mentioned above). If views have to be explicitly
requested that may not be a problem because the app author will
(hopefully) understand the issues. But even if it was just a standard
library module, I would worry that many inexperienced programmers
would complicate their code by using the string views module without
real benefits. Sort of the way some folks have knee-jerk habits to

  def foo(x, None=None):

if they use None anywhere in the body of the function. This should be
done only as a last resort when real-life measurements have shown that
foo() is a performance show-stopper.

--Guido van Rossum (home page: http://www.python.org/~guido/)

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