[Python-3000] range() issues

[Guido van Rossum]

On Wed, Apr 30, 2008 at 4:14 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Guido van Rossum wrote:
>
> >
> > On Wed, Apr 30, 2008 at 3:49 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
> wrote:
> >
> >
> >
> > > So that code will silently behave as though the rest of
> > > the sequence wasn't there some of the time?
> > >
> >
> > Only if it uses LBYL.
> >
>
>  I don't understand that. Iteration isn't the only thing
>  one does with sequences. If you have a reason to call
>  len() in the first place, I don't see how having it
>  sometimes return inaccurate results can be helpful.

I've come across situations where len() raising an exception was more
inconvenient than returning a truncated value (e.g. when printing).

> > > Can you elaborate on the rationale for this?
> > >
> >
>
>
> > Ask the designers of the Java collections package.
> >
>
>  Do you mean that they have a rationale which you agree
>  with and think applies to Python as well, or do you
>  mean that you're doing it just because Java does it
>  and they must have a good reason?
>
>  If the former, can you refer me to a document which
>  espouses it?

You'll have to do some research, but I believe the circumstances are
similar -- they have a size() method that is defined to return an
unboxed int, so they are limited by that.

I found the spec here:

http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html#size()

But I didn't find a rationale. I'm sure it was PBP though.

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