[Python-Dev] PEP 279

[Aahz]

On Thu, Mar 28, 2002, Guido van Rossum wrote:
>
>    Very confusing.  I propose to remove the start/stop arguments, *or*
>    change the spec to:
> 
>      def iterindexed(sequence, start=0, stop=None):
>          i = start
>          while stop is None or i < stop:
>              try:
>                  item = sequence[i]
>              except IndexError:
>                  break
>              yield (i, item)
>              i += 1
> 
>    This reduces the validity to only sequences (as opposed to all
>    iterable collections), but has the advantage of making
>    iterindexed(x, i, j) iterate over x[i:j] while reporting the index
>    sequence range(i, j) -- not so easy otherwise.
> 
>    The simplified version is still attractive because it allows
>    arbitrary iterators to be passed in:
> 
>      def iterindexed(collection):
>        i = 0
>        it = iter(collection)
>        while 1:
>          yield (i, it.next())
>          i += 1

How about doing it both ways: if you try to pass start/stop for an
iterator instead of a sequence, you get an AttributeError on
__getindex__.  (I'm not proposing this, just throwing it out as an
idea.  It does make explaining it more difficult, which is an argument
against.)
-- 
Aahz (aahz@pythoncraft.com)           <*>         http://www.pythoncraft.com/

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