def groups_option(f):
    new_func = click.option("-g", "--groups",
                            help="Comma-separated list of requirement groups "
                            "to include.")(f)
    return update_wrapper(new_func, f)
def _getN(self, n):
        n -= 1
        p = self.head
        while n:
            p = p.next
            n -= 1
        return p