On Mar 5, 12:28 pm, Steven D'Aprano <st...@remove-this- cybersource.com.au> wrote: > On Fri, 05 Mar 2010 18:12:05 +0000, Arnaud Delobelle wrote: > >>>> l = range(10) > >>>> l > > [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] > >>>> l[7::-1] > > [7, 6, 5, 4, 3, 2, 1, 0] > >>>> [l[i] for i in range(7, -1, -1)] > > [7, 6, 5, 4, 3, 2, 1, 0] > > Where does the first -1 come from? Slices are supposed to have default > values of 0 and len(seq):
The only way to get a 0 from a reverse range() is to have a bound of -1. > > >>> l[7::1] > [7, 8, 9] > >>> [l[i] for i in range(7, len(l), 1)] > [7, 8, 9] > >>> [l[i] for i in range(7, len(l), -1)] > > [] > > I don't believe the actual behaviour is documented anywhere. Well, it's implied. If the stopping bound in a reverse range() is greater than the starting bound, you get an empty return. > > -- > Steven -- http://mail.python.org/mailman/listinfo/python-list
