On Tue, Oct 13, 2015 at 11:26:09AM -0400, Random832 wrote: > "R. David Murray" <[email protected]> writes: > > > On 2015年10月13日 14:59:56 +0300, Stefan Mihaila > > <[email protected]> wrote: > >> Maybe it's just python2 habits, but I assume I'm not the only one > >> carelessly thinking that "iterating over an input a second time will > >> result in the same thing as the first time (or raise an error)". > > > > This is the way iterators have always worked. > > It does raise the question though of what working code it would actually > break to have "exhausted" iterators raise an error if you try to iterate > them again rather than silently yield no items.
Anything which looks like this: for item in iterator: if condition: break do_this() ... for item in iterator: do_that() If the condition is never true, the iterator is completely processed by the first loop, and the second loop is a no-op by design. I don't know how common it is, but I've written code like that. Had we been designing the iterator protocol from scratch, perhaps we might have had two exceptions: class EmptyIterator(Exception): ... class StopIteration(EmptyIterator): ... and have StopIteration only raised the first time you call next() on an empty iterator. But would it have been better? I don't know. I suspect not. I think that although it might avoid a certain class of errors, it would add complexity to other situations which are currently simple. -- Steve _______________________________________________ Python-Dev mailing list [email protected] https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com