[Python-Dev] PEP 435: initial values must be specified? Yes

[Tim Delaney]

On 6 May 2013 06:09, Ethan Furman <ethan at stoneleaf.us> wrote:

> On 05/05/2013 10:07 AM, � wrote:> I'm chiming in late, but am I the only
> one who's really bothered by the syntax?
>
>>
>> class Color(Enum):
>>      red = 1
>>      green = 2
>>      blue = 3
>>
>
> No, you are not only one that's bothered by it.  I tried it without
> assignments until I discovered that bugs are way too easy to introduce.
>  The problem is a successful name lookup looks just like a name failure,
> but of course no error is raised and no new enum item is created:
>
> --> class Color(Enum):
> ...     red, green, blue
> ...
>
> --> class MoreColor(Color):
> ...     red, orange, yellow
> ...
>
> --> type(MoreColor.red) is MoreColor
> False
>
> --> MoreColor.orange
> <MoreColor.orange: 4>   # value should be 5
>

Actually, my implementation at  https://bitbucket.org/magao/enum (the one
mentioned in the PEP) does detect MoreColor.red as a duplicate. It's
possible to do it, but it's definitely black magic and also involves use of
sys._getframe() for more than just getting module name.

>>> from enum import Enum
>>> class Color(Enum):
...     red, green, blue
...
>>> class MoreColor(Color):
...     red, orange, yellow
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".\enum.py", line 388, in __new__
    raise AttributeError("Duplicate enum key '%s.%s' (overriding '%s')" %
(result.__name__, v.key, k
eys[v.key]))
AttributeError: Duplicate enum key 'MoreColor.red' (overriding 'Color.red')
>>>

So long as I can get one of the requirements documented to implement an
auto-number syntax I'll be happy enough with stdlib enums I think.

class Color(AutoIntEnum):
    red = ...
    green = ...
    blue = ...

Not as pretty, but ends up being less magical.

Tim Delaney
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