[Python-Dev] Lockstep iteration - eureka!

[M.-A. Lemburg]

Guido van Rossum wrote:
> 
> > On Wed, 9 Aug 2000, Greg Ewing wrote:
> > >
> > >    for (x in a, y in b):
> > >       ...
> 
> No, for exactly the reasons Ping explained.  Let's give this a rest okay?
> 
> > I would much rather petition now to get indices() and irange() into
> > the built-ins... please pretty please?
> 
> I forget what indices() was -- is it the moreal equivalent of keys()?

indices() and irange() are both builtins which originated from
mx.Tools. See:

	http://starship.python.net/crew/lemburg/mxTools.html

* indices(object) is the same as tuple(range(len(object))) - only faster
and using a more intuitive and less convoluted name.

* irange(object[,indices]) (in its mx.Tools version) creates
a tuple of tuples (index, object[index]). indices defaults
to indices(object) if not given, otherwise, only the indexes
found in indices are used to create the mentioned tuple -- and
this even works with arbitrary keys, since the PyObject_GetItem()
API is used.

Typical use is:

for i,value in irange(sequence):
    sequence[i] = value + 1


In practice I found that I could always use irange() where indices()
would have been used, since I typically need the indexed
sequence object anyway.

> That's range(len(s)), I don't see a need for a new function.  In fact
> I think indices() would reduce readability because you have to guess
> what it means.  Everybody knows range() and len(); not everybody will
> know indices() because it's not needed that often.
> 
> If irange(s) is zip(range(len(s)), s), I see how that's a bit
> unwieldy.  In the past there were syntax proposals, e.g. ``for i
> indexing s''.  Maybe you and Just can draft a PEP?

-- 
Marc-Andre Lemburg
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