On Wed, May 20, 2015 at 3:46 AM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > On Wed, 20 May 2015 01:59 am, Marko Rauhamaa wrote: > >> Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info>: >> >>> To be useful, explanations ought to give the user *predictive power* >>> -- if I calculate 32767 + 1, what will Python do? >>> >>> Explanation #1 predicts that Python will return 32768. >>> Explanation #2 makes no prediction at all. >> >> Any semantic ruleset that correctly predicts the behavior of any given >> Python program is equally valid. > > This is a more reasonable position to take than your earlier stance that the > only thing that matters is whether it explains observed behaviour. It's > still wrong, but at least it is defensible in the sense that sometimes a > ruleset which is objectively wrong but still gives the right answer might > be *preferred* over one which is objectively correct but hard to > understand.
Perfect parallel with Magic: The Gathering, where a card may have reminder text on it which is, in the strictest sense of the definition, inaccurate, but covers 99%+ of situations without being horrendously wordy. The fundamental rulebook (the "Comp Rules") goes into excruciating detail, and is about as readable as the CPython source code (that is: pretty readable, but too verbose to use as documentation). For example, the "First Strike" ability is described simply as "This creature deals combat damage before creatures without first strike" [1], but the Comp Rules explain how there are two combat damage steps, and detail what happens if a creature gains or loses First Strike during combat. Even worse, "Madness" is described as "If you discard this card, you may cast it for its madness cost instead of putting it into your graveyard" [2]; the Comp Rules divide this into two parts, explaining in full how the card actually gets from one place to another, where it's cast from, and so on. Both of these reminder texts are technically inaccurate, but are massively preferred over the full text, because they actually fit inside your brain. Same thing happens with networking; when you go to https://www.python.org/ in a web browser, your browser establishes an encrypted connection with the server at www.python.org, and requests the "/" page. Well, actually, first there are DNS lookups, and IP routing, and TCP handshakes, and then the whole "establishes an encrypted connection" bit elides a ton of work involving certificate checks and so on... but it's much easier to just talk in very high level terms, even if it's not perfectly accurate. As predictive power goes, this explanation will adequately tell you what to expect a request for https://github.com/Rosuav to do; that makes it useful. An explanation that's more accurate is better than one that's less accurate; an explanation that's more complicated is worse than one that's simpler. Somewhere in the middle is an optimal descriptive style for a given situation. ChrisA [1] http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=134753 [2] http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=382849 -- https://mail.python.org/mailman/listinfo/python-list
