flying sheep added the comment: Hi, and sorry David, but I think you haven’t understood what I was proposing.
Maybe that was too much text and detail to read at once, while skipping the relevant details: Python has iterators and iterables. iterators are non-reentrant iterables: once they are exhausted, they are useless. But there are also iterables that create new, iterators whenever iter(iterable) is called (e.g. implicitly in a for loop). They are reentrant. This is why you can loop sequences such as lists more than once. ——————————————————————— One of those reentrant iterables is range(), whose __iter__ functions creates new lazy iterables, which has a __len__, and so on. It even has random access just like a sequence. Now it’s always entirely possible to *lazily* determine len(chain(range(200), [1,2,5])), which is of course len(range(200)) + len([1,2,5]) = 200 + 3 = 203. No reentrant iterables are necessary here, only iterables with a __len__. (Simply calling len() on them all is sufficient, as it could only create a TypeError which would propagate upwards) ——————————————————————— To reiterate: 1. Lazy doesn’t mean non-reentrant, just like range() demonstrates. 2. I didn’t propose that this works on arbitrary iterables, only that it works if you supply iterables with suitable properties (and throws ValueError otherwise, just like len(some_generator_function()) already does) 3. I know what I’m doing, please trust me and read my proposal carefully ;) ---------- resolution: rejected -> status: closed -> open _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue24849> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
