On Sun, Oct 31, 2021 at 7:10 PM Steven D'Aprano <st...@pearwood.info> wrote: > > On Tue, Oct 26, 2021 at 08:59:51AM +0100, Rob Cliffe via Python-ideas wrote: > > > And I don't understand what point you're making here. Yes, the walrus > > operator can appear in various places, how is that relevant? You could write > > def f(a := (b := c)): > > which might be a tad confusing but would be unambiguous and legal, just as > > def f(a = (b := c)): > > is currently legal (I tested it). I don't see a clash. > > If we have a choice between a dozen syntax variants that are not > confusing, and one which is confusing, why would we prefer to pick the > one that is confusing over any of the others? > > > > Perhaps I wasn't clear. When I said 'inefficiency', I meant to refer to > > cases like > > def f(a := b+1, b := e+1, c := a+1, d := 42, e := d+1) > > where late-binding defaults are allowed to refer to subsequent > > arguments. Here Python has to work out to assign first to d, then e, > > then b, then a, and finally c, which AFAICS requires multiple passes. > > No, I don't think we need to do anything that intricate. It is not the > responsibility of the interpreter to **make it work** no matter what, > any more than we expect the interpreter to make this work: > > a = b + 1 > b = e + 1 > c = a + 1 > d = 42 # <<<<<-----start here > e = d + 1 > > It is enough to have a simple rule: > > - bind early bound defaults left to right first; > - bind late bound defaults left to right next. > > (That's my preference.) Even simpler would be a strictly left-to-right > single pass but that would be, I think, too simple. YMMV. I'm not > prepared to fight to the death over that one :-) >
My current implementation uses the two-pass system, but only because that's simpler to code. Philosophically, I would prefer a one-pass system. What I will say is: I'm not going to lock the language into the two-pass system, and other Python implementations, or future versions of CPython, should be free to go one-pass. In any case, I have yet to see any examples that depend on two-pass that I wouldn't have rejected in code review. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/KYJ5HZWS4SRHJGHS4QHATYKU2CGUMTX4/ Code of Conduct: http://python.org/psf/codeofconduct/
