It is by design. `sorted` returns a list, while `reversed` returns an iterator. Iterators are exhaust-able, and not reusable. So be mindful of this and if you are going to "re-use” the sequence returned by iterator, convert it to list first.
Have a look at `itertools` library, which contains a lot of such functions and many good recipes on achieving various things elegantly using iterators. > On 1 Sep 2023, at 19:15, Pierre Fortin via Python-list > <python-list@python.org> wrote: > > Hi, > > reversed() results are fine until iterated over, after which the > results are no longer available. This was discovered after using > something like this: > > rev = reversed( sorted( list ) ) > sr = sum( 1 for _ in rev ) > # rev is now destroyed > > So reversed() results can only be iterated once unlike sorted(), etc... > > Script to illustrate the issue: > /tmp/rev: > orig = [ 'x', 'a', 'y', 'b', 'z', 'c' ] > co = sum( 1 for _ in orig ) > print( 'orig', orig, co ) > # reversing > rev = reversed(orig) > print( 'before iteration:', [ x for x in rev ] ) > # list comprehension was an iteration over 'rev' > print( 'after iteration:', [ x for x in rev ] ) > # how this was discovered... > orig = [ 'x', 'a', 'y', 'b', 'z', 'c' ] > rev = reversed(orig) > cr = sum( 1 for _ in rev ) > print( 'after sum():', [ x for x in rev ] ) > > which produces: > > $ python /tmp/rev > orig ['x', 'a', 'y', 'b', 'z', 'c'] 6 > before iteration: ['c', 'z', 'b', 'y', 'a', 'x'] > after iteration: [] > after sum(): [] > > Regards, > Pierre > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
