Hello,
On Mon, 06 Nov 2017 17:58:47 +0000
Brett Cannon <brett@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.
I don't think you meant for this to come off as insulting, but telling me how to look up the definition of an associative array or map feels like you're putting me down. I also have a Ph.D. in computer science so I'm aware of the academic definitions of these data structures.
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 don't think it's fair to call the current dict implementation a hack. It's a sound design that has a certain property that we are discussing the masking of. As I said previously, I think this discussion comes down to whether we think there are pragmatic benefits to exposing the ordered aspects to the general developer versus not.
-Brett
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@gmail.com