[Python-ideas] Fwd: Allow Enum members to refer to each other during execution of body

[Ethan Furman]

On 07/14/2013 02:36 PM, Antony Lee wrote:
> Is there any specific reason why you do not wish to change the behavior of Enum to this one (which does seem more
> logical to me)?  The patch is fairly simple in its logic (compared to the rest of the implementation, at least...),
> and I could even change it to remove the requirement of defining __new__ before the members as long as there are no
> references to other members (because as long as there are no references to other members, I obviously don't need to
> actually create the members), thus making it fully compatible with the current version.

My apologies for the delay in replying.

Getting Enum into the stdlib was a very careful balancing act:

     - Make it powerful enough to meet most needs as-is

     - Make it extensible enough that custom enumerations could be
       easily implemented

     - Make it simple enough to not create a large cognitive burden

How this relates to your patch:

1)  With your patch, referencing another enum member either returns
     the member itself (pure Enum), or the value of the Enum (mixed
     Enum) -- which means two different behaviors from the same
     syntax.

2)  The patch fails with the pure Enum with auto-numbering test case.
     It fails because __new__ is looking at the __member__ data
     structure which is empty for the duration of __prepare__.  While
     work arounds are possible, they would not be simpler, or even as
     simple.

Summary:  The resulting behavior is inconsistent, and the complexity added to the code, but mostly to the mind, is much 
greater than the minor benefit.

--
~Ethna