[Python-Dev] PEP-435 reference implementation

Guido van Rossum guido at python.org
Wed May 1 18:43:33 CEST 2013

On Wed, May 1, 2013 at 9:18 AM, Tres Seaver <tseaver at palladion.com> wrote:
> I'd be glad to drop both of those in favor of subclassing:  I think the
> emphasis on "class-ness" makes no sense, given the driving usecases for
> adopting enums into the stdlib in the first place.   IOW, I would vote
> that real-world usecases trump hypothetical purity.

Yeah, this is the dilemma. But what *are* the real-world use cases?
Please provide some.

Here's how I would implement "extending" an enum if subclassing were
not allowed:

class Color(Enum):
  red = 1
  white = 2
  blue = 3

class ExtraColor(Enum):
  orange = 4
  yellow = 5
  green = 6

flag_colors = set(Color) | set(ExtraColor)

Now I can test "c in flag_colors" to check whether c is a flag color.
I can also loop over flag_colors. If I want the colors in definition
order I could use a list instead:

ordered_flag_colors = list(Color) + list(ExtraColor)

But this would be less or more acceptable depending on whether it is a
common or esoteric use case.

--Guido van Rossum (python.org/~guido)

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