[Python-Dev] PEP 435: initial values must be specified? Yes
v+python at g.nevcal.com
Tue May 7 06:58:39 CEST 2013
On 5/6/2013 7:58 PM, Tim Delaney wrote:
> On 7 May 2013 12:29, Ethan Furman <ethan at stoneleaf.us
> <mailto:ethan at stoneleaf.us>> wrote:
> On 05/05/2013 02:55 PM, Tim Delaney wrote:
> 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 = ...
> Will this do?
> class AutoNumber(Enum):
> def __new__(cls):
> value = len(cls.__enum_info__) + 1
> obj = object.__new__(cls)
> obj._value = value
> return obj
> def __int__(self):
> return self._value
> class Color(AutoNumber):
> red = ()
> green = ()
> blue = ()
> Considering that doesn't actually work with the reference
> implementation (AutoNumber.__new__ is never called) ... no.
Maybe you should have tried with the latest version of the reference
implementation, where Ethan kindly fixed the reference implementation to
work better with NamedInt (per my thread "ref impl disc 2") and
apparently also with the above class's __new__...
> ---------- Run Python3 ----------
> Traceback (most recent call last):
> File "D:\home\repos\mercurial\ref435\ref435.py", line 292, in <module>
> TypeError: __int__ returned non-int (type tuple)
> Plus I would not want to use the empty tuple for the purpose - at
> least ... implies something ongoing.
Why not? For classes derived from Enum, having __new__, the value/tuple
assigned to the enumeration member becomes the set of parameters to
__new__... so why would you want to provide a parameter? Well, you
could, with a minor tweak. If you don't like Ethan's AutoNumber class,
you can now write your own, like the following one that I derived from
his, but to use your preferred ...
def __new__(cls, parm):
obj = object.__new__(cls)
if parm is ...:
value = len(cls.__enum_info__) + 1
obj._value = value
obj._value = parm
red = ...
green = ...
blue = 7
purple = ...
print ( Color.red, repr( Color.red ))
print ( Color.green, repr( Color.green ))
print ( Color.blue, repr( Color.blue ))
print ( Color.purple, repr( Color.purple ))
Since you want to provide a parameter, I decided in my example
AutoNumber class that I would use ... as a flag to use his count, and
anything else would be an actual value for the enumeration member. You
could do whatever else you like, of course, should you write your own,
including using someone's suggested itertools.count()
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