On 10/16/07, David A. Wheeler <[EMAIL PROTECTED]> wrote: > Hi, I'm a Python user who likes much in the upcoming Python 3000. I wish you > well! I have a few comments, though, that I hope are constructive. Guido > asked me to repost them to this mailing list for discussion. I'll send my > different comments as separate messages, so that they can be easily discussed > separately. So... > > In PEP 3119 (Abstract Base Classes): I suggest adding an ABC for a > "generalized bool" (perhaps name it Gbool?). > > Any class defining __bool__ (formerly __nonzero__), or one implementing Sized > (which implement __len__), would be a generalized boolean. (Well, unless > __len__ is no longer auto-called if there's no __bool__; if there's no > auto-call, then I think just __bool__ would be checked, similar to how Sized > works). All numbers and collections are generalized bools, obviously; many > user-created classes will NOT be generalized bools. Many functions accept > generalized bools, not strictly bools, and it'd be very nice to be able to > explicitly _denote_ that in a standard way.
This sounds misguided to me. While it is true that some types can never be false, they can still be useful as a truth value: e.g. a parameter could be either a Widget object (assuming Widgets are never false) or None. This is used pretty commonly. So there is absolutely nothing to test for in the type of an object -- *every* object is usable as a "generalized boolean". It therefore becomes purely a matter of argument annotation, an area which is explicitly left open for experimentation by PEP 3107. -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
