On Tue, 21 Jun 2022 at 01:44, MRAB <pyt...@mrabarnett.plus.com> wrote: > > On 2022-06-20 15:05, Chris Angelico wrote: > > On Mon, 20 Jun 2022 at 21:11, Jonathan Fine <jfine2...@gmail.com> wrote: > >> > >> Hi > >> > >> Some have liked adding a new syntax > >> a, b, ... = iterable > >> to mean consume two items from the iterable. However, > >> a, b, Ellipsis = iterable > >> has a different meaning (at least in Python 3.8). It redefines Ellipsis. > >> (As an explicit constant, '...' can be redefined.) > > > > To clarify: The syntactic token '...' will always refer to the special > > object Ellipsis (at least back as far as Python 3.4 - can't remember > > when it became available in all contexts), but the name Ellipsis can > > be rebound. So even though, in many contexts, "x = Ellipsis" and "x = > > ..." will have the same net effect, they are distinct (one is a name > > lookup and the other is a constant), and they're definitely different > > in assignment. > > > > (Though it wouldn't surprise me if a future Python release adds > > Ellipsis to the set of non-assignable names, with None/True/False.) > > > >> The syntax > >> a, b, ... = iterable > >> so to speak fills a gap in existing syntax, as the construct is at present > >> invalid. I actually like gaps in syntax, for the same reason that I like a > >> central reservation in a highway. The same goes for the hard shoulder / > >> breakdown lane. > >> > >> The title of this thread includes the phrase 'Stop Iterating' (capitals > >> added). This suggests the syntax > >> a, b, StopIterating = iterable > >> where StopIterating is a new keyword that can be used only in this context. > >> > >> I'd like to know what others think about this suggestion. > >> > > > > Hard no. That is currently-legal syntax, and it's also clunky. I'd > > much rather the "assign to ..." notation than a weird new soft keyword > > that people are going to think is a typo for StopIteration. > > > > It's worth noting that the proposed syntax has a slight distinction > > from the normal asterisk notation, in that it makes perfect sense to > > write this: > > > > a, *_, b = thing > > > > but does not make sense to write this: > > > > a, ..., b = thing > > > > as the "don't iterate over this thing" concept doesn't work here. > > (Supporting this would require some way to reverse the iterator, and > > that's not a language guarantee.) > > > It could be taken to mean "consume but discard", leaving 'a' bound to > the first item and 'b' bound to the last item, but then: > > a, ... = thing > > would have to leave 'a' bound to the first item and the iterator exhausted. > > In fact, use of ... would always have to exhaust the iterator, which, I > think, would not be very useful. > > Best not to go that way.
Yeah. "Consume but discard" is spelled *_, so we don't need this. The whole point of this is to NOT consume it. 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/NJFEUDVYWP5QIAB4WS7P6IWJDW7TEBM2/ Code of Conduct: http://python.org/psf/codeofconduct/
