[Python-Dev] PEP 435: initial values must be specified? Yes (original) (raw)

Tim Delaney timothy.c.delaney at gmail.com
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 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.

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