On Oct 5, 10:23 am, Joost Cassee <[EMAIL PROTECTED]> wrote: > Hello all, > > I bumped into an unexpected problem using generators. Consider this code: > > def test(s): > return _test([], [], s) > def _test(s1, s2, s): > if s: > s1.append(s.pop()) > for x in _test(s1, s2, s): > yield x > s2.append(s1.pop()) > for x in _test(s1, s2, s): > yield x > s.append(s2.pop()) > else: > yield s1, s2
Lists aren't copied when they're yielded, so you're returning the same lists (with different elements) each time. Your final list looks like [(s1, s2), (s1, s2), ...] and as it happens, s1 and s2 are both [] by the end. You can fix it by copying the lists manually before yielding them, or using a better sub-list algorithm :) -- Paul Hankin -- http://mail.python.org/mailman/listinfo/python-list
