[Python-Dev] constant/enum type in stdlib

[Guido van Rossum]

On Tue, Nov 23, 2010 at 11:47 AM, Barry Warsaw <barry at python.org> wrote:
> On Nov 23, 2010, at 05:02 PM, Michael Foord wrote:
>
>>> * Enums are not subclassed from ints or strs.  They are a distinct data type
>>>    that can be converted to and from ints and strs.  EIBTI.
>>
>>But if we are to use it *in* the standard library (as opposed to merely
>>adding a module *to* the standard library) there are backwards compatibility
>>concerns. Where modules are already using integers for constants then
>>integers still need to work.
>
> Is int(enum_value) enough, or must the enum value actually *be* an int?

I vote for *be*, following bool's example.

>>One easy way to achieve this is to subclass integer. If we don't do that
>>(assuming we decide that putting a solution in the standard library is
>>appropriate) then we'll have to evaluate what we mean by backwards
>>compatible. If the modules that use the constants aren't to change then
>>comparing equal to the underlying value is the minimum (so that the original
>>value can still be used in place of the new named constant). Not sure if
>>you'd be happy to make that change in flufl.enum.
>
> I'm not sure either.  In flufl.enum enum_class(i) also works as expected.
>
>>> * The typical way to create them is through a simple, but explicit class
>>>    definition.  I personally like being explicit about the item values, and
>>>    the assignments are required to make the metaclass work properly, but
>>>    Michael's convenience patch is totally appropriate for cases where you
>>>    don't care, or you want a one-liner.
>>
>>If make_enum was to take a set of values to use (as Antoine suggested) I
>>don't see what's un-explicit about it.
>
> When I saw your patch I immediately thought that I could add a default
> argument that was something like `int_iter`, i.e. an iterator of integers for
> the values in the string.  I suspect YAGNI, which is why I didn't just add it,
> but I'm not totally opposed to it.
>
> -Barry
>
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--Guido van Rossum (python.org/~guido)