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

[Thomas Nyberg]

On 11/07/2017 09:00 AM, Wolfgang wrote:
> Hi,
> 
> I have to admit sometimes I don't understand why small things produce so much
> mail traffic. :-)
> 
> If I use a mapping like dict most of the time I don't care if it is ordered.
> If I need an ordering I use OrderedDict. In a library if I need a dict to be
> ordered most of the time there is a parameter allowing me to do this or to
> specify the used class as dict.
> If this is not the case it can be fixed. In rare cases a workaround is needed.
> 
> As of now I have dict and OrderedDict, it is clear and explicit.
> No need to change.
> 
> 	[...]
>
> Regards,
> 
> Wolfgang

I feel a bit out of place on this list since I'm a lurker and not a core
developer, but I just wanted to add my agreement with this as well. So
maybe take my opinion with a grain of salt...

I agree with Wolfgang. I just don't understand why this change is
needed. We have dict and we have OrderedDict. Why does dict need to
provide the extra ordering constraints? I've read many posts in this
discussion and find none of them convincing. Python already guarantees
things like ordering of keyword arguments. I've seen some people point
out confusion of newcomers (e.g. they are surprised when order is not
surprised), but that just seems to me natural confusion that comes about
when learning. I would argue that a better solution to that problem is
exactly the go solution: i.e. purposely perturbing the ordering in a way
that shows up immediately so that users realize the problems in their
thinking earlier. The dict provides a mapping from key to value. I
personally think that that is mentally much simpler object than a
mapping from key to value with certain ordering guarantees. If I want to
extra guarantees I import OrderedDict and read what the guarantees are.
This seems totally fine to me. I don't really see any advantages to this
change but a lack of implementation flexibility and a more complicated
core object in Python.

Cheers,
Thomas