[Python-Dev] enum discussion: can someone please summarize open issues?

Cameron Simpson cs at zip.com.au
Mon Apr 29 08:36:15 CEST 2013

On 28Apr2013 19:46, Ethan Furman <ethan at stoneleaf.us> wrote:
| int, float, and bool all have object constructors that take the
| given string and return a matching instance; int /may/ return a
| pre-existing instance, bool /will/ return a pre-existing instance.

I think Guido's already pointed out this:

  >>> bool('False')

| As I've stated before, 'bool's are the closest existing data type to
| enums, in that bools use the object constructor to convert the
| incoming parameter to an existing bool instance, of which there will
| only ever be two.
| bool(9) is bool('maybe') is bool(True) is True
| and similarly, Enum behavior /should be/ (in my opinion ;)
| Season.AUTUMN is Season('AUTUMN') is Season(3)

I think that would be _efficient_, but as an outside user I wouldn't
necessarily expect it unless I'd ready the spec very closely and
the spec was explicit about it.

Coming from (in the fairly distant past) a C background, I naively
think of enums as nicely named ordinals of some kind and expect to
compare them with ==, not "is".

If you want to guarantee "is", be my guest though.
I don't know how that might make things go with some hypothetical subclass
with many many and extensible enum values.

| Like it or not, when you write `class Season(Enum)` a new *type* is
| created called Season, and Season(x) should either return a Season
| instance that matches x or raise.  Having a match and raising anyway
| just doesn't seem to me to be the Python Way.

I'm +1 on all of this.

| >I'm not sure whether flufl.enums support creating additional instances after the event, but if it did, I would expect
| >that I could say Season('WET') to get a new instance. I am indifferent to whether or not Season('AUTUMN') should return
| >the existing AUTUMN enum value.
| Adding more enumerators after the fact should not be supported;
| there is subclassing for that. Not worth actively preventing, but
| not encouraged.

I'd go a bit further here: I'd take this final sentence as being
-0 on preventing adding more enumerals(?), whereas I'm a solid -1
on preventing it. By all means not actively support it, but very
against doing things that make it hard for a subclass to support

Just 2c,

Would you remember a one-line .sig?     - Paul Thompson, thompson at apple.com

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