Greg Ewing writes:
On 16/04/22 10:46 pm, Steven D'Aprano wrote:
There is no *guessing* in the C3 linearization algorithm.
"Guessing" in the context of that Zen line means making an arbitrary choice that may or may not be what the programmer wants. It doesn't mean choosing at random.
Every feature means making an arbitrary choice that may or may not be what the programmers wanted. That's why we sometimes rewrite stuff in C: because most applications of "such stuff" we want time or space performance more than we want the dynamic power of Python. But we have a requirement (at least a strong suggestion) that where possible C modules should also provide Python implementations so that people who want the power of Python can have it, at some cost in performance. So in the context of the Zen, I suggest we "refuse to guess" *because* that arbitrary choice also forecloses (or at least makes very difficult) other choices. Otherwise, that Zen would discourage adding any features at all! But to me, C3 is hardly arbitrary. The technical sense in which a deterministic algorithm doesn't guess is irrelevant to the Zen, as you point out. But I don't think that's what Steven meant. Someone wrote that C3 is based on 5 requirements, which could also be considered assumptions about what the programmer wants. I don't recall what they are exactly, but they seemed really plausible to me as a guide to what most programmers would want, or at least find acceptable, most of the time. If you're going to call something even in the event of multiple definitions, C3 has benefits (I don't have time to enumerate them right now). I don't think that's an arbitrary guess, and I think that's what Steven meant. But still, what if that's not what the programmer wants? Can they get what they want, *as easily as if the feature didn't exist*? How often does it happen that they can't? I haven't seen any compelling answers to those questions, only cooked-up toy programs whose only known use is to give the answer "yes" to the question "can I find a program where super() and/or C3 can't do the thing I arbitrarily prespecify that the program must do?", and one (1) hearsay story whose "harm" is perfectly well redressed by "OK, don't fix what ain't broke, then". Steve