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

Tue May 7 07:14:25 CEST 2013

On 7 May 2013 14:54, Ethan Furman <ethan at stoneleaf.us> wrote:
> On 05/06/2013 07:58 PM, Tim Delaney wrote:
>>>>> Considering that doesn't actually work with the reference implementation
>> (AutoNumber.__new__ is never called) ... no.
>>>> Two points:
>> 1) Did you grab the latest code? That exact implementation passes in
> the tests.
>
D'oh! I had my default path being my forked repo ... so didn't see the
changes. BTW I can't see how that exact implementation passes ... not
enough parameters declared in AutoNumber.__new__ ...
> 2) You can write your __new__ however you want -- use ... ! ;)

 class AutoNumber(Enum):
 def __new__(cls, value):
 if value is Ellipsis:
 try:
 value = cls._auto_number
 except AttributeError:
 value = cls._auto_number = 0
 else:
 cls._auto_number = int(value)
 obj = object.__new__(cls)
 obj._value = value
 cls._auto_number += 1
 return obj
 def __int__(self):
 return self._value
 class Color(AutoNumber):
 red = ...
 green = 3
 blue = ...
 print(repr(Color.red))
 print(repr(Color.green))
 print(repr(Color.blue))
---------- Run Python3 ----------
<Color.red: 0>
<Color.green: 3>
<Color.blue: 4>
Unfortunately, if you subclass AutoNumber from IntEnum it breaks.
---------- Run Python3 ----------
Traceback (most recent call last):
 File "D:\home\repos\mercurial\ref435\ref435.py", line 346, in <module>
 class Color(AutoNumber):
 File "D:\home\repos\mercurial\ref435\ref435.py", line 184, in __new__
 enum_item = __new__(enum_class, *args)
TypeError: int() argument must be a string or a number, not 'ellipsis'
I would probably also suggest 2 changes:
1. Set enum_item._name before calling enum_item.__init__.
2. Don't pass any arguments to enum_item.__init__ - the value should be set
in enum_item.__new__.
Tim Delaney
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