python中多层循环的一键退出

a=[‘a‘,1,2,3,4]
b=[‘b‘,1,2,3,4]
c=[‘c‘,1,2,3,4]
d=[‘d‘,1,2,3,4]
break_flag=0
while break_flag==0:
    y_n=input(‘a,yes or no:‘)
    if y_n == ‘n‘:
        break
    elif y_n == ‘y‘:
        for i in a:
            print(i)
        while break_flag ==0:
            y_n_2=input(‘b,yes or no:‘)
            if y_n_2==‘n‘:
                print(‘退出‘)
                break_flag=1
            elif y_n_2==‘y‘:
                for i in b:
                    print(i)
                while break_flag==0:
                    y_n_3=input(‘c,yes or no:‘)
                    if y_n_3 == ‘n‘:
                        print(‘退出。。。‘)
                        break_flag=1
                    elif y_n_3 == ‘y‘:
                        for i in c:
                            print(i)