Re: Infinitely nested containers

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From	Ian Kelly <ian.g.kelly@gmail.com>
Date	Fri, 21 Nov 2014 11:37:29 -0700
Subject	Re: Infinitely nested containers
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On Fri, Nov 21, 2014 at 10:39 AM,  <random832@fastmail.us> wrote:
> On Fri, Nov 21, 2014, at 02:00, Marko Rauhamaa wrote:
>> Gill Shen <gillarete@gmail.com>:
>>
>> > How is this [nesting] behavior implemented under the hood?
>>
>> Pointers.
>>
>> > And why is this allowed at all?
>>
>> There's no reason not to.
>
> There's no reason not to allow it with tuples, but you can't do it.
> Mainly because doing it in a single literal would require special
> syntax, whereas you can simply append to a list a reference to itself.
>
> I think I tried on at least one python version and printing the tuple
> crashed with a recursion depth error, since it had no special protection
> for this case the way list printing does.

Here's a nice crash. I thought this might similarly produce a
recursion depth error, but no, it's a seg fault!

$ cat test.py
import itertools

l = []
it = itertools.chain.from_iterable(l)
l.append(it)
next(it)
$ python3 test.py
Segmentation fault (core dumped)

Thread

Infinitely nested containers Gill Shen <gillarete@gmail.com> - 2014-11-20 21:54 -0800
  Re: Infinitely nested containers Marko Rauhamaa <marko@pacujo.net> - 2014-11-21 09:00 +0200
    Re: Infinitely nested containers random832@fastmail.us - 2014-11-21 12:39 -0500
      Re: Infinitely nested containers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-22 15:43 +1100
        Re: Infinitely nested containers Chris Angelico <rosuav@gmail.com> - 2014-11-22 15:50 +1100
          Re: Infinitely nested containers Rustom Mody <rustompmody@gmail.com> - 2014-11-21 21:02 -0800
            Re: Infinitely nested containers Chris Angelico <rosuav@gmail.com> - 2014-11-22 16:09 +1100
              Re: Infinitely nested containers Rustom Mody <rustompmody@gmail.com> - 2014-11-21 22:03 -0800
        Re: Infinitely nested containers Ethan Furman <ethan@stoneleaf.us> - 2014-11-22 11:50 -0800
          Re: Infinitely nested containers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-23 16:59 +1100
            Re: Infinitely nested containers random832@fastmail.us - 2014-11-23 01:39 -0500
    Re: Infinitely nested containers Chris Angelico <rosuav@gmail.com> - 2014-11-22 04:47 +1100
    Re: Infinitely nested containers random832@fastmail.us - 2014-11-21 12:50 -0500
    Re: Infinitely nested containers Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-21 11:37 -0700
    Re: Infinitely nested containers Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-11-21 13:30 -0600
    Re: Infinitely nested containers Terry Reedy <tjreedy@udel.edu> - 2014-11-22 16:57 -0500
  Re: Infinitely nested containers Chris Angelico <rosuav@gmail.com> - 2014-11-21 18:03 +1100
  Re: Infinitely nested containers Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-21 10:13 -0700

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