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

[Glenn Linderman]

On 4/25/2013 3:23 PM, Barry Warsaw wrote:
> My point is, "days of the week" has a natural ordering, so why wouldn't you
> use IntEnum for that?  Problem solved.

While the ordering is natural, some implementations start from 0, some 
start from 1, and on the naming side, some start from Sunday, and some 
start from Monday. So there are lots of opportunities for the numbers 
vary, and having easy conversions to int which expose those numbers and 
allow comparisons to integers, is adding problems, not solving them.


On 4/25/2013 3:36 PM, Ethan Furman wrote:
> People like things sorted (or am I alone here?)  There are three 
> obvious natural orderings:
>
>   1 - value
>
>   2 - definition order
>
>   3 - name
>
> And that's my order of preference for them. 

So, being blissfully unaware of the implementation issues, not having 
yet read the implementation, I suggest that the preferred iteration 
order should be a characteristic of the Enum when defined, and/or that 
there should be a method to obtain a list in any of the natural 
orderings (specifying value ordering may add a restriction that the 
values be orderable, if done at definition time; if done only on 
retrieval, attempting to access the list by value would raise an exception).

Another possible ordering would be "random", and for enumerations with 
values that are tuples or lists or hashes, ordering by some specified 
element would be conceivable. On the other hand, except for "definition" 
order, all the other possible orderings could be derived externally to 
the enumeration.

So if enumerations preserve/provide "definition" order, all the others 
could be implemented externally or as subtypes. "Definition" order, then 
is the basic ordering for enumerations because it cannot be externally 
derived, other than by reading the source code.

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