知识点： 异常之raise

raise语句手工引发一个异常:

1 "raise" [expression ["," expression ["," expression]]] 

 

 

try:
    for i in range(3):
        for j in range(3):
            if i==2:
                raise KeyboardInterrupt  #手动引发异常
            print(i,j)
except KeyboardInterrupt:
    print("退出啦")