[Python-ideas] constant/enum type in stdlib

[Eli Bendersky]

On Wed, Jan 30, 2013 at 7:35 AM, Barry Warsaw <barry at python.org> wrote:

> On Jan 30, 2013, at 03:16 PM, Michael Foord wrote:
>
> >Being an int subclass (and possibly optionally a strs subclass) is a
> >requirement if any adopted Enum is to be used *within* the standard
> library
> >in places where integers are currently used as "poor man's enums". I also
> >don't *think* flufl.enum supports flag enums (ones that can be OR'd
> >together), right?
>
> Sure, it does because you have to be explicit about the enum int value to
> assign the item.  This doesn't bother me because the syntax is clear, I
> almost
> always want an explicit int value anyway, inheritance is supported, and as
> you
> comment, flag values are (mostly) easy to support.
>
> class Colors(Enum):
>     red = 1
>     green = 2
>     blue = 3
>
> class MoreColors(Colors):
>     cyan = 4
>     magenta = 5
>     # chartreuse = 2 would be an error
>
> class Flags(Enum):
>     beautiful = 1
>     fast = 2
>     elegant = 4
>     wonderful = 8
>
>
> Now, it's true that because Flags.fast is not an int, it must be explicitly
> converted to an int, e.g. `int(Flags.fast)`.  That doesn't bother me.
>
> What does bother me is that Enum doesn't support automatic conversion to
> int
> for OR and AND, so you have to do this:
>
> >>> int(Flags.fast) | int(Flags.elegant)
> 6
>
> That should be easy enough to fix by adding the appropriate operators so
> that
> you could do:
>
> >>> Flags.fast | Flags.elegant
> 6
>
> Returning an int from such operations is the only sensible interpretation.
>
> https://bugs.launchpad.net/flufl.enum/+bug/1110501
>
> As far as autonumbering goes, I think we could support that in Python 3.3+,
> though I don't have any brilliant ideas on syntax.  A couple of suggestions
> are in this bug:
>
> https://bugs.launchpad.net/flufl.enum/+bug/1110507
>
> e.g
>
> class Colors(Enum):
>     red = None
>     green = None
>     blue = None
>
> or
>
> from flufl.enum import Enum, auto
> class Colors(Enum):
>     red = auto
>     green = auto
>     blue = auto
>
> I'm definitely open to suggestions here!
>

Barry, since you've obviously given this issue a lot of thought, maybe you
could summarize it in a PEP so we have a clear way of moving forward for
3.4 ?

Eli
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