[Python-Dev] PEP 246: lossless and stateless

[Phillip J. Eby]

At 05:32 PM 1/15/05 +0100, Just van Rossum wrote:
>Phillip J. Eby wrote:
>
> > >It's not at all clear to me that "sticky" behavior is the best
> > >default behavior, even with implicit adoptation. Would anyone in
> > >their right mind expect the following to return [0, 1, 2, 3, 4, 5]
> > >instead of [0, 1, 2, 0, 1, 2]?
> > >
> > >   >>> from itertools import *
> > >   >>> seq = range(10)
> > >   >>> list(chain(islice(seq, 3), islice(seq, 3)))
> > >   [0, 1, 2, 0, 1, 2]
> > >   >>>
> >
> > I don't understand why you think it would.  What does islice have to
> > do with adaptation?
>
>islice() takes an iterator, yet I give it a sequence.

No, it takes an *iterable*, both practically and according to its 
documentation:

 >>> help(itertools.islice)
Help on class islice in module itertools:

class islice(__builtin__.object)
  |  islice(iterable, [start,] stop [, step]) --> islice object
  |
  | ... [snip rest]

If you think about the iterator and iterable protocols a bit, you'll see 
that normally the adaptation goes the *other* way: you can pass an iterator 
to something that expects an iterable, as long as it doesn't need 
reiterability.