Hi all, Thanks for the explanation. Now I agree that the need for list.rindex() is not as common as str.rindex(). In fact, I only need list.rindex() when doing some algorithm problems. I guess that doesn't count as real need here.
Best, John Lin Guido van Rossum <gu...@python.org> 於 2019年4月24日 週三 上午4:20寫道： > On Tue, Apr 23, 2019 at 1:02 PM MRAB <pyt...@mrabarnett.plus.com> wrote: > >> On 2019-04-23 18:52, Terry Reedy wrote: >> > On 4/23/2019 2:44 AM, 林自均 wrote: >> >> Hi all, >> >> >> >> I found that there are str.index() and str.rindex(), but there is only >> >> list.index() and no list.rindex(). >> > >> > str.index and list.index are related but not the same. The consistency >> > argument is better applied to find-rfind, index-rindex, >> > partition-rpartition, etc. >> > >> > It is much more common to process strings right to left or in both >> > directions, than process lists right to left or in both directions. >> > Moreover, lists have a reverse method, strings do not. >> > ''.join(reversed(somestring)) is likely slower, especially if there many >> > non-ascii chars. Moreover, somestring.rindex(substring) would have to >> > have both somestring and substring reversed when substring is more than >> > one char. >> > >> You can reverse a string with somestring[::-1]. >> >> Personally, I'm not convinced by the "lists can be reversed" argument. >> > > Me neither, though for substring checks, reversing the string would be > even more cumbersome (you'd have to reverse the query string too). > > My money is on "nobody uses this for lists". > > Some use cases for rindex() on strings that I found in a large codebase > here include searching a pathname for the final slash, a list of > comma-separated items for the last comma, a fully-qualified module name for > the last period, and some ad-hoc parsing of other things. The "last > separator" use cases are the most common and here rindex() sounds very > useful. > > -- > --Guido van Rossum (python.org/~guido) > *Pronouns: he/him/his **(why is my pronoun here?)* > <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/> > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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