[Python-Dev] Guarantee ordered dict literals in v3.7?

[Chris Barker]

On Tue, Dec 19, 2017 at 8:14 AM, Barry Warsaw <barry at python.org> wrote:

> On Dec 18, 2017, at 22:37, Nathaniel Smith <njs at pobox.com> wrote:
>
> > Wait, what? Why would changing pprint (so that it accurately reflects
> > dict's new underlying semantics!) be a breaking change? Are you
> > suggesting it shouldn't be changed in 3.7?
>
> As others have pointed out, exactly because the current behavior is
> documented.  And we all know that if it’s documented (and often even if
> it’s not, but that’s besides the point here) it will be relied upon.
>

Nathaniel Smith has pointed out that  eval(pprint(a_dict)) is supposed to
return the same dict -- so documented behavior may already be broken.

(though I assume order is still ignored when comparing dicts, so:
eval(pprint(a_dict))
== a_dict will still hold.

But practicality beats purity, and a number of folks have already posted
use-cases where they rely on sorted order, so there you go.


> So we can’t change the default behavior.  But I have no problems
> conceptually with giving users options.  The devil is in the details
> though, e.g. should we special case dictionary sorting only?



> Should we use a sort `key` to mirror sorted() and list.sort()?
>

That would be a nice feature! If anything is done, I think we should allow
a key function.

and maybe have key=None as "unsorted"

-CHB




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