Josh Rosenberg <shadowranger+pyt...@gmail.com> added the comment:
Remi: The reason they're not hashable is presumably because it would make them valid dictionary keys, further confusing the difference between sequences and mappings. x[::-1] would, for a sequence, return a reversed sequence, but for a mapping, would end up using the slice as a key (not actually slicing) to obtain a single value. Confusing at best. Serhiy: It was discussed on the other issue, but the rationale there was, to quote Raymond: * too many other things need to be changed to support it * the measured win is somewhat small * we have a negative bias towards expanding the peephole optimizer * the AST may be a better place to do these kind of optimizations Of those, only the first bullet is (essentially) unchanged. Addressing the following points in order: * The win will likely be higher given that the __getslice__ protocol no longer exists; where slice objects need not be constructed in many cases in Python 2 (which had the SLICE+N bytecodes to perform subscripting directly, without a separate code to build a slice), leaving only slices with a step dependent on actually building slices. Nowadays, x[:-1] requires building a slice object, as does x[1:] and the like, where previously they did not * The approach I'm taking does not use the peephole optimizer in any way * I'm making the changes in the AST optimizer Perhaps the issues with "too many other things need to be changed" remain, but I'd like to at least have a PR in place so that, should the marshalling format change be accepted, we'd be able to take advantage of it. Side-note: The marshal code for marshalling slices that I chose was ':'; seemed rather appropriate for slices, and conveniently, it was not already in use. :-) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue11107> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
