[Python-ideas] Fwd: Re: Unambiguous repr for recursive objects

[Guido van Rossum]

On Sat, Dec 26, 2015 at 10:19 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 27 December 2015 at 07:05, Andrew Barnert via Python-ideas
> <python-ideas at python.org> wrote:
> > At any rate, I think what people are actually worried about here is not
> the theoretical chance that such a regression might have happened 5 years
> ago, but the more practical fact that 3.x might be misleading to human
> beings in cases where 2.x wasn't. For example, if you mostly do 3.x NumPy
> stuff, you're used to passing ellipses around, and maybe even storing them
> in index arrays, but you rarely if ever see a circular list. So, when you
> see, say, `[[1], [2], [...]]` on the REPL, you may misinterpret it as
> meaning something different from what it does.
>
> Right, this is the reason I think it's reasonable to suggesting
> changing the recursive repr - the current form is one that *humans*
> that have only learned Python 3 are likely to misinterpret, since the
> fact that "repr(...)"produces "Ellipsis" rather than "..." is itself a
> quirk originating in the fact that "..." is restricted to subscripts
> in Python 2.
>
> I don't think it's a major problem (as recursive container
> representations aren't something that comes up every day), but
> switching to "<...>" does have the advantage of allowing for a
> consistent recursive reference representation across all container
> types, regardless of whether they have native syntax or not.
>

I really feel you all are overworrying and overthinking this. A downside to
me is that <...> isn't clear about what the type of the object is. The use
case here is not sophisticated users, it's beginners who have accidentally
managed to create a recursive list or dict. They have most likely not even
encountered Ellipsis objects yet. There's nothing clearer than the current
notation to help them see that they've done something unusual.

-- 
--Guido van Rossum (python.org/~guido)
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