python 八皇后问题

import random
def conflict(state,nextx):
    nexty = len(state)
    for i in range(nexty):
        if abs(state[i]-nextx) in (0,nexty-i):
            return True
    return False
def queens(num=8,state=()):
    for pos in range(num):
        if not conflict(state,pos):
            if len(state) == num - 1:
                yield (pos,)---------------------------------------------------------当前面三个（1,3,0）都满足，最后一行满足条件，比如为2时，返回的是(2,)就终止循环了，请问（2，）是怎么添加到元组中，变成（1,3,0，2）的？
            else:
                for result in queens(num,state + (pos,)):
                    yield (pos,) + result