On 10/08/2013 05:15 PM, Steven D'Aprano wrote: > On Wed, Oct 09, 2013 at 01:33:26AM +0200, Larry Hastings wrote: >> >> The obvious solution: add a new singleton constant to Python >> that is passed in when a parameter is not mapped to an argument. >> I propose that the value be called called ``undefined``, >> and be a singleton of a special class called ``Undefined``. >> If a positional-only parameter did not receive an argument >> when called, its value would be set to ``undefined``. > > I would much prefer Undefined and UndefinedType. That matches other > singletons like None, NotImplemented, Ellipsis, even True and False. The type of Ellipsis is ellipsis, and the type of True and False is bool. ;) That aside, I agree that Undefined and UndefinedType would be better. > What (if any) methods and attributes would Undefined have? If it doesn't > have any, doesn't that make it functionally equivalent to None? Why not > just use None? The PEP needs to explain why it needs to invent yet > another singleton that quacks like None. I think the key question here is are there places where None is the passed in value, and its meaning is something besides "no value passed in". I don't know the answer. > [Bikeshed: perhaps Missing is more appropriate than Undefined? After > all, the parameter is defined, only the value is missing.] Or the value is undefined. ;) -- ~Ethan~
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