[Python-Dev] Python 3.6 dict becomes compact and gets a private version; and keywords become ordered

[Gregory P. Smith]

On Mon, Sep 12, 2016 at 10:25 AM INADA Naoki <songofacandy at gmail.com> wrote:

>
> So fundamental question is: Is it to so bad thing that some people
> write code depending on CPython and PyPy implementation?
>

Yes.  See below.

I think cross-interpreter libraries can use OrederedDict correctly
> when they should use it. (They may run test on micropython, Jython and
> IronPython).
>

The problem is that libraries which could otherwise be cross-VM compatible
are not because they depend upon an implementation detail. So it becomes an
additional porting burden on people trying to use the library on another VM
that could've been avoided if we required people to be explicit about their
needs.

BUT...

At this point I think coding up an example patch against beta1 offering a
choice of disordered iteration capability that does not increase memory or
iteration overhead in any significant way is needed.

The problem is... I don't know how to express this as an API. Which sinks
my whole though process and tables the idea.

A parameter to .items(), .keys() and .values() is undesirable as it isn't
backwards compatible [meaning it'll never be used] and .keys() needs to
match __iter__ which can't have one anyways. A parameter on dict
construction is similarly infeasible.

Requiring the use of an orderdict like type in order to get the behavior is
undesirable. Effectively I'm asking for some boolean state in each dict as
to if it should iterate in order or not and a way to expose that to pure
Python code in a way that namespace dicts iterate in order by default and
others do not unless explicitly configured to do so.

oh well.  end thought process on my end.  it was good while it lasted.

Thanks for the compact and ordered dicts! People will love them. :)

-gps
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