I'm sorry, but unless there's a sudden landslide of support for 'given' in favor of ':=', I'm really not going to consider it.
I'd pronounce "if (x := y) > 0" as either "if y (assigned to x) is greater than zero" or "if x (assigned from y) is greater than zero". On Thu, May 10, 2018 at 6:39 AM, Nick Coghlan <ncogh...@gmail.com> wrote: > On 8 May 2018 at 04:19, Brett Cannon <br...@python.org> wrote: > >> My brain wants to drop the variable name in front of 'given': >> >> if given m = pattern.search(data): >> >> while given m = pattern.search(remaining_data): >> >> Maybe it's because the examples use such a short variable name? >> > > Does that change if the condition isn't just "bool(name)"? For example: > > if y > 0 given y = f(x): > ... > > That's the situation where I strongly prefer the postfix operator > spelling, since it's pretty clear how I should pronounce it (i.e. "if y is > greater than zero, given y is set to f-of-x, then ..."). By contrast, while > a variety of plausible suggestions have been made, I still don't really > know how to pronounce "if (y := f(x)) > 0:)" in a way that's going to be > clear to an English-speaking listener (aside from pronouncing it the same > way as I'd pronounce the version using "given", but that then raises the > question of "Why isn't it written the way it is pronounced?"). > > I do agree with Tim that the name repetition would strongly encourage the > use of short names rather than long ones (since you're always typing them > at least twice), such that we'd probably see code like: > > while not probable_prime(n) given (n = > highbit | randrange(1, highbit, 2)): > pass > > Rather than the more explicit: > > while not probable_prime(candidate) given (candidate = > highbit | randrange(1, highbit, 2)): > pass > > However, I'd still consider both of those easier to follow than: > > while not probable_prime(candidate := highbit | randrange(1, highbit, > 2)): > pass > > since it's really unclear to me that "candidate" in the latter form is a > positional argument being bound to a name in the local environment, and > *not* a keyword argument being passed to "probable_prime". > > I've also been pondering what the given variant might look like as a > generally available postfix operator, rather than being restricted to > if/elif/while clauses, and I think that would have interesting implications > for the flexibility of its usage in comprehensions, since there would now > be *three* places where "given" could appear (as is already the case for > the inline binding operator spelling): > > - in the result expression > - in the iterable expression > - in the filter expression > > That is: > > [(x, y, x - y) given y = f(x) for x in data] > [(x, data) for x in data given data = get_data()] > [(x, y, x/y) for x in data if y given y = f(x)] > > Rather than: > > [(x, y := f(x), x - y) for x in data] > [(x, data) for x in data := get_data()] > [(x, y, x/y) for x in data if y := f(x)] > > Opening it up that way would allow for some odd usages that might need to > be discouraged in PEP 8 (like explicitly preferring "probable_prime(n) > given n = highbit | randrange(1, highbit, 2)" to "probable_prime(n given n > = highbit | randrange(1, highbit, 2))"), but it would probably still be > simpler overall than attempting to restrict the construct purely to > if/elif/while. > > Even as a generally available postfix keyword, "given" should still be > amenable to the treatment where it could be allowed as a variable name in a > non-operator context (since we don't allow two adjacent expressions to > imply a function call, it's only prefix keywords that have to be disallowed > as names to avoid ambiguity in the parser). > > Cheers, > Nick. > > -- > Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > > -- --Guido van Rossum (python.org/~guido)
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