This might of been suggested in the other thread, but,
Instead of going after the built-in set why not propose a collections
based OrderedSet akin to OrderedDict? I would believe that might be less
contentious.
On 24/08/2020 23:43, Cade Brown wrote:
Hello all,
I have a suggestion/idea for the Python standard (and/or a CPython
implementation detail, considering its memory impact): having sets
behave similar to dictionaries in that they preserve first-appearance
order (i.e. dictionaries are ordered by key which was first inserted).
As is said in the Python standard, a 'set' is by definition unordered.
Yet, internally they must be stored in some order, and when iterated
upon, converted to string, etc, some ordering must be used. Right now,
it is unspecified, which can lead to interesting results I noticed:
>>> print ({1, 2, 3}, {3, 2, 1})
{1, 2, 3} {1, 2, 3}
>>> print ({1, 5, 9}, {9, 5, 1})
{1, 5, 9} {9, 5, 1}
While, obviously, things like `A == B` are not affected by this, many
algorithms may affect their output if sets are treated as iterables
(again, the argument could be made, as it was for 'dict' as well, that
they should not treat the order as relevant at all). Further, I
believe that having a specification regarding the order and some
guarantees could be useful and important to cohesiveness of Python as
a whole.
Despite the obvious non-ordered nature of sets, I still think it is
worth making them behave like `dict` objects (which are also, in some
sense, 'unordered' by nature, and yet Python still specifies the order
for 3.7+).
I would like to suggests that `set` objects are ordered by insertion,
so that:
* Sets have a defined, repeatable order for maximum reproducibility
(assuming the code generates the set in a stable way)
* Tests which are outside of Python can do string comparisons and
expect the same output each time (as with `dict` objects generated in
a predictable way).
* On a high-level note, Python specifies more exact behavior. It is
my belief (and I'm sure many others share this as well) that
unspecified/implementation-dependent/otherwise-undependable features
should be eliminated and replaced with exact semantics that do not
suprise users.
Thoughts?
Thanks,
~
Cade Brown
Working on MAGMA <https://icl.cs.utk.edu/magma/>
http://cade.site
http://chemicaldevelopment.us
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