[Python-Dev] PEP-435 reference implementation (original) (raw)

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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