[Python-3000] range() issues (original) (raw)

Guido van Rossum guido at python.org
Thu May 1 01:41:22 CEST 2008

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/)

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