[Python-Dev] constant/enum type in stdlib

[Michael Foord]

On 23/11/2010 14:16, Nick Coghlan wrote:
> On Tue, Nov 23, 2010 at 11:50 PM, Michael Foord
> <fuzzyman at voidspace.org.uk>  wrote:
>> PEP 354 was rejected for two primary reasons - lack of interest and nowhere
>> obvious to put it. Would it be *so bad* if an enum type lived in its own
>> module? There is certainly more interest now, and if we are to use something
>> like this in the standard library it *has* to be in the standard library
>> (unless every module implements their own private _Constant class).
>>
>> Time to revisit the PEP?
> If you (or anyone else) wanted to revisit the PEP, then I would advise
> trawling through the standard library looking for constants that could
> be sensibly converted to enum values.
>
> A decision would also need to be made as to whether or not to subclass
> int, or just provide __index__ (the former has the advantage of being
> able to drop cleanly into OS level APIs that expect a numerical
> constant).
>
> Whether enums should provide arbitrary name-value mappings (ala C
> enums) or were restricted to sequential indices starting from zero
> would be another question best addressed by a code survey of at least
> the stdlib.
>
> And getgeneratorstate() doesn't count as a use case, since the
> ordering isn't needed and using string literals instead of integers
> will cover the debugging aspect :)
>
Well, for backwards compatibility reasons the new constants would have 
to *behave* like the old ones (including having the same underlying 
value and comparing equal to it).

In many cases it is *likely* that subclassing int is a better way of 
achieving that. Actually looking through the standard library to 
evaluate it is the only way of confirming that.

Another API, that reduces the duplication of creating the enum and 
setting the names, could be something like:

     make_enums("Names", "NAME_ONE NAME_TWO NAME_THREE", base_type=int, 
module=__name__)

Using __name__ we can set the module globals in the call to make_enums.

All the best,

Michael


> Cheers,
> Nick.
>


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