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Re: Strange range

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On Friday, April 1, 2016 at 10:34:50 AM UTC-4, Marko Rauhamaa wrote:
> Chris Angelico <rosuav@gmail.com>:
> 
> > *A range object is not an iterator.*
> 
> We now have learned as much.
> 
> However, doesn't that extra level of indirection seem like an odd
> choice?

I agree that it is surprising (and confusing) at first.  It took me
some getting used to.

Now I think of it like this: An iterable is a thing that could be
iterated, that is, it has a sequence of things.  An iterator holds the
current status of a thing that is being iterated.  For example, the
pages of a book are an iterable (we could iterate over them), and a
bookmark is an iterator for the pages of a book: it knows where we are
in the iteration.

This analogy illuminates an important point: a single iterable can have
a number of active iterators working over it at once, just as a book can
have a number of bookmarks in it at once.

    nums = [1, 2, 3]
    for i in nums:
        for j in nums:
            print i, j

This prints all the pairs of numbers, because the iterator in the first
loop is independent of the iterator(s) in the second loop, even though
they are iterating over the same iterator (the nums list).  Without the
extra indirection of iterators over iterables, this code would get
tangled up.

--Ned.

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Thread

Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 16:15 +0300
  Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-02 00:24 +1100
  Re: Strange range Steven D'Aprano <steve@pearwood.info> - 2016-04-02 00:26 +1100
    Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 17:12 +0300
      Re: Strange range Random832 <random832@fastmail.com> - 2016-04-01 10:39 -0400
    Re: Strange range Fabien <fabien.maussion@gmail.com> - 2016-04-01 16:16 +0200
      Re: Strange range Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-01 17:28 +0300
      Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-02 01:31 +1100
        Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 17:34 +0300
          Re: Strange range Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-01 17:44 +0300
          Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-02 01:45 +1100
            Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 18:43 +0300
          Re: Strange range Erik <python@lucidity.plus.com> - 2016-04-01 20:58 +0100
            Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 23:14 +0300
              Re: Strange range Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2016-04-01 20:21 +0000
                Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 23:44 +0300
              Re: Strange range Steven D'Aprano <steve@pearwood.info> - 2016-04-02 21:09 +1100
                Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-02 13:48 +0300
          Re: Strange range Ned Batchelder <ned@nedbatchelder.com> - 2016-04-02 12:47 -0700
            Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-02 23:44 +0300
              Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-03 07:05 +1000
                Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-03 00:40 +0300
                Re: Strange range Ned Batchelder <ned@nedbatchelder.com> - 2016-04-02 14:50 -0700
                Re: Strange range Stephen Hansen <me+python@ixokai.io> - 2016-04-02 23:43 -0700
                Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-03 09:58 +0300
                Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-03 17:10 +1000
                Re: Strange range Ethan Furman <ethan@stoneleaf.us> - 2016-04-03 09:28 -0700
                Re: Strange range Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-04-04 13:21 +0100
                Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-03 17:08 +1000
              Re: Strange range Steven D'Aprano <steve@pearwood.info> - 2016-04-03 14:43 +1000
                Re: Strange range Random832 <random832@fastmail.com> - 2016-04-03 01:20 -0400
                Re: Strange range Steven D'Aprano <steve@pearwood.info> - 2016-04-03 15:28 +1000
      Re: Strange range Marko Rauhamaa <marko@pacujo.net> - 2016-04-01 17:32 +0300
  Re: Strange range Random832 <random832@fastmail.com> - 2016-04-01 10:42 -0400
  Re: Strange range Chris Angelico <rosuav@gmail.com> - 2016-04-02 01:50 +1100
  Re: Strange range Ian Kelly <ian.g.kelly@gmail.com> - 2016-04-01 08:52 -0600

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