[Python-3000] Need help completing ABC pep (original) (raw)

Guido van Rossum guido at python.org
Sat Apr 21 17:06:37 CEST 2007

On 4/21/07, Phillip J. Eby <pje at telecommunity.com> wrote:

At 12:33 PM 4/20/2007 -0700, Talin wrote: >Additionally, the need to override the classification of an >object can be done more cleanly using generic functions: In the simplest >case, one can define a "category membership" generic function that >simply returns False in the base implementation, and then provide >overrides that return True for any classes of interest.

Yes, but that's sort of like saying it's better to point a pistol at your foot than a shotgun. :) Explicitly testing category membership is a bug, not a feature; you're far better off defining an overload to do whatever it was you were going to make the if-then test do.

I don't believe that's always true. I can imagine use cases where, if I were writing it in an if-then-else fashion, I'd be writing the same if-test several times as part of a particular algorithm, without having an easy way to refactor the algorithm so that there's only one place testing it. Turning each place where the if-test is repeated into a different GF might be a wasted of time; turning just the test into a GF seems just right. (IN THAT PARTICULAR CASE.)

Note that I don't object against the idea that usually a GF is better; I just don't think it always is so.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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