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

[Paul Sokolovsky]

Hello,

On Mon, 06 Nov 2017 17:58:47 +0000
Brett Cannon <brett at python.org> wrote:

[]

> > Why suddenly once in 25 years there's a need to do something to
> > dict's, violating computer science background behind them (one of
> > the reason enough people loved Python comparing to other "practical
> > hack" languages)?
> 
> I don't understand what "computer science background" is being
> violated?

I tried to explain that in the previous mail, can try a different
angle. So, please open you favorite CS book (better few) and look up
"abstract data types", then "mapping/associative array" and "list". We
can use Wikipedia too: https://en.wikipedia.org/wiki/Associative_array.
So, please look up: "Operations associated with this data type allow".
And you'll see, that there're no "ordering" related operations are
defined. Vice versa, looking at "sequence" operations, there will be
"prev/next", maybe "get n'th" element operations, implying ordering.

Python used to be a perfect application of these principles. Its dict
was a perfect CS implementation of an abstract associative array, and
list - of "sequence" abstract type (with additional guarantee of O(1)
random element access).

People knew and rejoiced that Python is built on solid science
principles, or could *learn* them from it. That no longer will be true,
with a sound concept being replaced with on-the-spot practical hack,
choosing properties of a random associative array algorithm
implementation over properties of a superset of such algorithms (many
of which are again don't offer any orderness guarantees).



I know though what will be replied (based on the replies below): "all
these are implementation details" - no, orderness vs non-orderness of a
mapping algorithm is an implementation detail; "users shouldn't know all
that" - they should, that's the real knowledge, and up until now, they
could learn that from *Python docs*, "we can't predict future" - we
don't need, we just need to know the past (25 years in our case), and
understand why it was done like that, I don't think Guido couldn't code
it ordered in 1991, it's just not natural for a mapping type to be so,
and in 2017, it's not more natural than it was in 1991.


MicroPython in particular appeared because Python offered all the
CS-sound properties and freedom and alternative choices for
implementation (more so than any other scripting language). It's losing
it, and not just for MicroPython's surprise.


[]


-- 
Best regards,
 Paul                          mailto:pmiscml at gmail.com