On Wed, May 1, 2013 at 10:48 AM, Guido van Rossum <gu...@python.org> wrote:
> On Wed, May 1, 2013 at 10:21 AM, Ethan Furman <et...@stoneleaf.us> wrote: > > We may not want to /completely/ disallow subclassing. Consider: > > > > --> class StrEnum(str, Enum): > > ... '''string enums for Business Basic variable names''' > > ... > > --> class Vendors(StrEnum): > > EnumError: subclassing not allowed > > > > > > My point is that IntEnum, StrEnum, ListEnum, FloatEnum are all > "subclasses" > > of Enum. To then have a subclass of > > that, such as Season(StrEnum), is subclassing a subclass. > > True, and Enum itself also falls in this category. Maybe there could > be a special marker that you have to set in the class body (or a > keyword arg in the class statement) to flag that a class is meant as a > "category of enums" rather than a specific enum type. Such categorical > classes should not define any instances. (And maybe "defines no > instances" is enough to flag an Enum class as subclassable.) > > > Now, if we do want to completely disallow it, we can ditch IntEnum and > force > > the user to always specify the mixin > > type: > > > > --> class Season(str, Enum): > > . > > . > > . > > > > --> class Names(str, Enum): > > . > > . > > . > > > > But that's not very user friendly... although it's not too bad, either. > > Indeed, given that we mostly want IntEnum as a last-resort backward > compatibility thing for os and socket, it may not be so bad. > > Actually, in flufl.enum, IntEnum had to define a magic __value_factory__ attribute, but in the current ref435 implementation this isn't needed, so IntEnum is just: class IntEnum(int, Enum): ''' Class where every instance is a subclass of int. ''' So why don't we just drop IntEnum from the API and tell users they should do the above explicitly, i.e.: class SocketFamily(int, Enum): AF_UNIX = 1 AF_INET = 2 As opposed to having an IntEnum explicitly, this just saves 2 characters (comma+space), but is more explicit (zen!) and helps us avoid the special-casing the subclass restriction implementation. Eli
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