code: def _inc_path(self):
          
          newpos = self._str2int(self.path[-self.steplen:]) + 1
          key = self._int2str(newpos)
          if len(key) > self.steplen:
              raise PathOverflow(_("Path Overflow from: '%s'" % (self.path, )))
          return '{0}{1}{2}'.format(
              self.path[:-self.steplen],
              self.alphabet[0] * (self.steplen - len(key)),
              key
          )
docs: :returns: The path of the next sibling of a given node path.