On 02.08.2014 08:35, Terry Reedy wrote: > On 8/2/2014 1:57 AM, Allen Li wrote: >> On Fri, Aug 01, 2014 at 02:51:54PM -0700, Guido van Rossum wrote: >>> No. We just can't put all possible use cases in the docstring. :-) >>> >>> >>> On Fri, Aug 1, 2014 at 2:48 PM, Andrea Griffini <agr...@tin.it> wrote: >>> >>> help(sum) tells clearly that it should be used to sum numbers >>> and not >>> strings, and with strings actually fails. >>> >>> However sum([[1,2,3],[4],[],[5,6]], []) concatenates the lists. >>> >>> Is this to be considered a bug? >> >> Can you explain the rationale behind this design decision? It seems >> terribly inconsistent. Why are only strings explicitly restricted from >> being sum()ed? sum() should either ban everything except numbers or >> accept everything that implements addition (duck typing). > > O(n**2) behavior, ''.join(strings) alternative. > >
hm could this be a pure python case that would profit from temporary elision [0]? lists could declare the tp_can_elide slot and call list.extend on the temporary during its tp_add slot instead of creating a new temporary. extend/realloc can avoid the copy if there is free memory available after the block. [0] https://mail.python.org/pipermail/python-dev/2014-June/134826.html _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
