'Returns another slice of this Index slice.
Parameters
item : slice
Index slice'

def __getitem__(self, item):

    if (self.length <= 0):
        return SlicedIndex(self.index, slice(1, 0))
    (start, stop, step) = item.indices(self.length)
    new_start = self.orig_coords(start)
    new_stop = self.orig_coords(stop)
    new_step = (self.step * step)
    return SlicedIndex(self.index, (new_start, new_stop, new_step))
