[Python-Dev] PEP 435 -- Adding an Enum type to the Python standard library

[Guido van Rossum]

Can we separate the iteration order and the comparison order? For
iteration order, I think by definition order or by attribute name are
both great, and better than by value. But for comparing values using
<, ==, >, I strongly feel we should defer to the underlying values --
if those cannot be compared, then the enums can't either, but the
iteration order is still defined.

On Sat, Apr 20, 2013 at 11:26 AM, R. David Murray <rdmurray at bitdance.com> wrote:
> On Sat, 20 Apr 2013 14:10:32 -0400, Barry Warsaw <barry at python.org> wrote:
>> On Apr 13, 2013, at 08:37 AM, Tim Delaney wrote:
>>
>> >Just using definition order as the stable iteration order would do the
>> >trick - no need for any comparisons at all. Subclasses (e.g. IntEnum) can
>> >then override it.
>>
>> I think this isn't possible if we want to keep backward compatibility with
>> earlier Pythons, which I want to do.  OTOH, we have another natural sorting
>> order for base Enums sitting right in front of us: the attribute name.  These
>> have to be unique and ordered, so why not use this for both the __repr__() and
>> the base Enum __iter__()?  IntEnum can override __iter__() to iterate over
>> item values, which also must be ordered.
>>
>> I just made this change to flufl.enum and it seems to work well.
>>
>> >>> from flufl.enum import Enum
>> >>> A = Enum('A', 'a b c')
>> >>> A
>> <A {a: 1, b: 2, c: 3}>
>> >>> for item in A: print(item)
>> ...
>> A.a
>> A.b
>> A.c
>> >>> B = Enum('B', 'c b a')
>> >>> B
>> <B {a: 3, b: 2, c: 1}>
>> >>> for item in B: print(item)
>> ...
>> B.a
>> B.b
>> B.c
>> >>> from flufl.enum import IntEnum
>> >>> C = IntEnum('C', 'c b a')
>> >>> C
>> <C {a: 3, b: 2, c: 1}>
>> >>> for item in C: print(item)
>> ...
>> C.c
>> C.b
>> C.a
>
> I think definition order would be much better, but if we can't have that,
> this is probably better than value order for non-int.
>
> --David
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-- 
--Guido van Rossum (python.org/~guido)