Brian Blais wrote: > On Jul 29, 2011, at 9:22 PM, Steven D'Aprano wrote: > >> Billy Mays wrote: >> >>> Is xrange not a generator? I know it doesn't return a tuple or list, so >>> what exactly is it? >> >> xrange pre-dates generators by approximately forever. It returns a >> special "xrange object", which generates values suitable for use in >> for-loops using the old __getitem__ protocol. >> > > interesting...I never really thought about this. Is there a reason that > it wasn't reimplemented when generators came out? Is there a use-case for > the current implementation that wouldn't work as a generator?
It certainly couldn't be re-implemented before Python 3, because that would change the behaviour and therefore break people's code that expected to be able to treat xrange objects as sequences. And now that Python 3.2 is out, and 3.3 is being worked on, it can't be changed now either, for the same reason. There was a very narrow window of opportunity for the functionality to be changed, and it was missed. Probably because nobody thought about it, but if it had been proposed to change xrange into an iterator, I'm pretty confident that the suggestion would have been rejected. xrange objects might be lazily generated, but they're also sequence types: you can get their length, and you can index them. (However you can't slice them.) Iterators are not sequence types: they aren't indexable and you can't get their length. So why bother *taking away* functionality from xrange just to make it a less powerful and more restricted iterator? It works fine just the way it is, there's no need to change it. It isn't like the Python developers are sitting around bored, looking for things to do. They are overworked with far too much to do and not enough manpower or time to do it. There are a huge number of much more important bug fixes and features that haven't been dealt with for them to bother with something like this. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
