[Python-3000] Making more effective use of slice objects in Py3k

Josiah Carlson jcarlson at uci.edu
Tue Aug 29 07:17:11 CEST 2006

"Guido van Rossum" <guido at python.org> wrote:
> Those are all microbenchmarks. It's easy to prove the superiority of
> an approach that way. But what about realistic applications? What if
> your views don't end up saving memory or time for an application, but
> still cost in terms of added complexity in all string operations?

At no point has anyone claimed that every operation on views will always
be faster than on strings.  Nor has anyone claimed that it will always
reduce memory consumption.  However, for a not insignificant number of
operations, views can be faster, offer better memory use, etc.

I agree with Jean-Paul Calderone:

"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."

"I don't think we see people overusing buffer() in ways which damage
readability now, and buffer is even a builtin.  Tossing something off
into a module somewhere shouldn't really be a problem.  To most people
who don't actually know what they're doing, the idea to optimize code
by reducing memory copying usually just doesn't come up."

While there are examples where views can be slower, this is no different
than the cases where deque is slower than list; sometimes some data
structures are more applicable to the problem than others.  As we have
given users the choice to use a structure that has been optimized for
certain behaviors (set and deque being primary examples), this is just
another structure that offers improved performance for some operations.

> Then I ask you to make it so that string views are 99.999%
> indistinguishable from strings -- they have all the same methods, are
> usable everywhere else, etc.

For reference, I'm about 2 hours into it (including re-reading the
documentation for Pyrex), and I've got [r]partition, [r]find, [r]index,
[r|l]strip. I don't see significant difficulty implementing all other
methods on views.

Astute readers of the original implementation will note that I never
check that the argument being passed in is a string; I use the buffer
interface, so anything offering the buffer interface can be seen as a
read-only view with string methods attached.  Expect a full
implementation later this week.

 - Josiah

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