On Mon, Apr 16, 2018 at 1:58 AM, Steven D'Aprano <st...@pearwood.info> wrote: > On Sun, Apr 15, 2018 at 10:21:02PM +1000, Chris Angelico wrote: > >> I don't think we're ever going to unify everyone on an arbitrary >> question of "expression first" or "name first". But to all the >> "expression first" people, a question: what if the target is not just >> a simple name? >> >> while (read_next_item() -> items[i + 1 -> i]) is not None: >> print("%d/%d..." % (i, len(items)), end="\r") > > I don't see why it would make a difference. It doesn't to me.
Okay, that's good. I just hear people saying "name" a lot, but that would imply restricting the grammar to just a name, and I don't know how comfortable people are with more complex targets. >> Does this make sense? With the target coming first, it perfectly >> parallels the existing form of assignment: > > Yes, except this isn't ordinary assignment-as-a-statement. > > I've been mulling over the question why I think the expression needs to > come first here, whereas I'm satisfied with the target coming first for > assignment statements, and I think I've finally got the words to explain > it. It is not just long familiarity with maths and languages that put > the variable first (although that's also part of it). It has to do with > what we're looking for when we read code, specifically what is the > primary piece of information we're initially looking for. > > In assignment STATEMENTS the primary piece of information is the target. > Yes, of course the value assigned to the target is important, but often > we don't care what the value is, at least not at first. We're hunting > for a known target, and only when we find it do we care about the value > it gets. > [chomp details] > It is appropriate for assignment statements and expressions to be > written differently because they are used differently. I don't know that assignment expressions are inherently going to be used in ways where you ignore the assignment part and care only about the expression part. And I disagree that assignment statements are used primarily the way you say. Frequently I skim down a column of assignments, caring primarily about the functions being called, and looking at the part before the equals sign only when I come across a parameter in another call; the important part of the line is what it's doing, not where it's stashing its result. > [...] >> >>> items = [None] * 10 >> >>> i = -1 >> >>> items[i := i + 1] = input("> ") >> > asdf >> >>> items[i := i + 1] = input("> ") >> > qwer >> >>> items[i := i + 1] = input("> ") >> > zxcv >> >>> >> >>> items >> ['asdf', 'qwer', 'zxcv', None, None, None, None, None, None, None] > > > I don't know why you would write that instead of: > > items = [None]*10 > for i in range(3): > items[i] = input("> ") > > > or even for that matter: > > items = [input("> ") for i in range(3)] + [None]*7 > > > but whatever floats your boat. (Python isn't just not Java. It's also > not C *wink*) You and Kirill have both fallen into the trap of taking the example too far. By completely rewriting it, you destroy its value as an example. Write me a better example of a complex target if you like, but the question is about how you feel about complex assignment targets, NOT how you go about creating a particular list in memory. That part is utterly irrelevant. >> Are you as happy with that sort of complex >> expression coming after 'as' or '->'? > > Sure. Ignoring the output of the calls to input(): The calls to input were in a while loop's header for a reason. Ignoring them is ignoring the point of assignment expressions. ChrisA _______________________________________________ Python-ideas mailing list Pythonfirstname.lastname@example.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/