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From: Serhiy Storchaka <storchaka@gmail.com>
Subject: Re: enhancement request: make py3 read/write py2 pickle format
Date: Thu, 11 Jun 2015 14:11:25 +0300
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Xref: csiph.com comp.lang.python:92463

On 11.06.15 02:58, Chris Angelico wrote:
> On Thu, Jun 11, 2015 at 8:10 AM, Devin Jeanpierre
> <jeanpierreda@gmail.com> wrote:
>> The problem is that there are two different ways repr might write out
>> a dict equal to {'a': 1, 'b': 2}. This can make tests brittle -- e.g.
>> it's why doctest fails badly at examples involving dictionaries. Text
>> format protocol buffers output everything sorted, so that you can do
>> textual diffs for compatibility tests and such.
>
> With Python's JSON module [1], you can pass sort_keys=True to
> stipulate that the keys be lexically ordered, which should make the
> output "canonical". Pike's Standards.JSON.encode() [2] can take a flag
> value to canonicalize the output, which currently has the same effect
> (sort mappings by their indices). I did a quick check for Ruby and
> didn't find anything in its standard library JSON module, but knowing
> Ruby, it'll be available somewhere in a gem.

AFAIK Ruby's dicts are ordered. So the output is pretty stable.