On Thu, 23 Jun 2022 at 08:56, Steve Jorgensen <stevec...@gmail.com> wrote: > > This is based on previous discussions of possible ways of matching all > remaining items during destructuring but without iterating of remaining final > items. This is not exactly a direct replacement for that idea though, and > skipping iteration of final items might or might not be part of the goal. > > In this proposal, the ellipsis (...) can be used in the expression on the > left side of the equals sign in destructuring anywhere that `*<varname>` can > appear and has approximately the same meaning. The difference is that when > the ellipsis is used, the matched items are not stored in variables. This can > be useful when the matched data might be very large. > > ..., last_one = <expression> > a, ..., z = <expression> > first_one, ... = <expression> > > Additionally, when the ellipsis comes last and the data is being retrieved by > iterating, stop retrieving items since that might be expensive and we know > that we will not use them. > > > Alternative A: > > Still iterate over items when the ellipsis comes last (for side effects) but > introduce a new `final_elipsis` object that is used to stop iteration. The > negation of `ellipsis` (e.g. `-...`) could return `final_ellipsis` in that > case. >
No need to have an object there - you could just define it as a syntactic construct instead. Assignment targets aren't themselves objects (although the same syntax can often be used on the RHS, when it would resolve to one). > Alternative B: > > Still iterate over items when the ellipsis comes last (for side effects) and > don't provide any new means of skipping iteration over final items. The > programmer can use islice to achieve that. > This is exactly equivalent to using star-underscore, minus the final step of assigning. Not really very advantageous. Having a way to say "allow additional elements without iterating over them" would be useful, but creating a new way to spell the non-assignment wouldn't be of sufficiently great value to justify the syntax IMO. 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/JJPVSXCDKGW6TPFFDF46G7CZB43DIMFO/ Code of Conduct: http://python.org/psf/codeofconduct/
