假設一段python程式有多重迴圈，我們都知道在乙個迴圈當中，用break是退出當前的迴圈，然後繼續下一次迴圈，但是如何才能跳出多重迴圈呢，實際就是結束所有的迴圈。
思路1：:可以定義乙個異常類，在需要退出迴圈的位置，跑出這個異常，就可以了，因為程式在遇到異常的時候，如果沒有捕獲異常的話，就是直接退出程式的執行，利用這個原理，認為的觸發乙個異常，然後把這個異常捕獲到，就可以實現退出多重迴圈，而且不結束程式，繼續往下執行
#encoding=utf-8
class getoutofloop(exception):
pass
try:
for i in range(5):
for j in range(5):
for k in range(5):
if i == j ==k ==3:
raise getoutofloop()#丟擲乙個異常，就會跳出所有迴圈
else:
print i,'---',j,'---',k
except getoutofloop:
pass
print "done"
結果：可以看到在迴圈到特定條件時，直接丟擲異常，然後進行捕獲，使程式跳出迴圈後並不結束，而是接著捕獲異常的位置後面繼續執行。
d:\>python test.py
0 --- 0 --- 0
0 --- 0 --- 1
0 --- 0 --- 2
0 --- 0 --- 3
0 --- 0 --- 4
0 --- 1 --- 0
0 --- 1 --- 1
0 --- 1 --- 2
0 --- 1 --- 3
0 --- 1 --- 4
0 --- 2 --- 0
0 --- 2 --- 1
0 --- 2 --- 2
0 --- 2 --- 3
0 --- 2 --- 4
0 --- 3 --- 0
0 --- 3 --- 1
0 --- 3 --- 2
0 --- 3 --- 3
0 --- 3 --- 4
0 --- 4 --- 0
0 --- 4 --- 1
0 --- 4 --- 2
0 --- 4 --- 3
0 --- 4 --- 4
1 --- 0 --- 0
1 --- 0 --- 1
1 --- 0 --- 2
1 --- 0 --- 3
1 --- 0 --- 4
1 --- 1 --- 0
1 --- 1 --- 1
1 --- 1 --- 2
1 --- 1 --- 3
1 --- 1 --- 4
1 --- 2 --- 0
1 --- 2 --- 1
1 --- 2 --- 2
1 --- 2 --- 3
1 --- 2 --- 4
1 --- 3 --- 0
1 --- 3 --- 1
1 --- 3 --- 2
1 --- 3 --- 3
1 --- 3 --- 4
1 --- 4 --- 0
1 --- 4 --- 1
1 --- 4 --- 2
1 --- 4 --- 3
1 --- 4 --- 4
2 --- 0 --- 0
2 --- 0 --- 1
2 --- 0 --- 2
2 --- 0 --- 3
2 --- 0 --- 4
2 --- 1 --- 0
2 --- 1 --- 1
2 --- 1 --- 2
2 --- 1 --- 3
2 --- 1 --- 4
2 --- 2 --- 0
2 --- 2 --- 1
2 --- 2 --- 2
2 --- 2 --- 3
2 --- 2 --- 4
2 --- 3 --- 0
2 --- 3 --- 1
2 --- 3 --- 2
2 --- 3 --- 3
2 --- 3 --- 4
2 --- 4 --- 0
2 --- 4 --- 1
2 --- 4 --- 2
2 --- 4 --- 3
2 --- 4 --- 4
3 --- 0 --- 0
3 --- 0 --- 1
3 --- 0 --- 2
3 --- 0 --- 3
3 --- 0 --- 4
3 --- 1 --- 0
3 --- 1 --- 1
3 --- 1 --- 2
3 --- 1 --- 3
3 --- 1 --- 4
3 --- 2 --- 0
3 --- 2 --- 1
3 --- 2 --- 2
3 --- 2 --- 3
3 --- 2 --- 4
3 --- 3 --- 0
3 --- 3 --- 1
3 --- 3 --- 2
done
思路2：在多重迴圈中用return，直接進行返回，程式遇到return就會認為程式執行結束，進而退出多個迴圈，這種情況，執行return後，程式不會繼續往下執行，而是直接結束程式
#encoding=utf-8
#函式中，用return會退出多重迴圈
def test():
for i in range(5):
for j in range(5):
for k in range(5):
if i ==j==k==3:
return
else:
print i,'---',j,'---',k
test()
結果：d:\>python test.py
0 --- 0 --- 0
0 --- 0 --- 1
0 --- 0 --- 2
0 --- 0 --- 3
0 --- 0 --- 4
0 --- 1 --- 0
0 --- 1 --- 1
0 --- 1 --- 2
0 --- 1 --- 3
0 --- 1 --- 4
0 --- 2 --- 0
0 --- 2 --- 1
0 --- 2 --- 2
0 --- 2 --- 3
0 --- 2 --- 4
0 --- 3 --- 0
0 --- 3 --- 1
0 --- 3 --- 2
0 --- 3 --- 3
0 --- 3 --- 4
0 --- 4 --- 0
0 --- 4 --- 1
0 --- 4 --- 2
0 --- 4 --- 3
0 --- 4 --- 4
1 --- 0 --- 0
1 --- 0 --- 1
1 --- 0 --- 2
1 --- 0 --- 3
1 --- 0 --- 4
1 --- 1 --- 0
1 --- 1 --- 1
1 --- 1 --- 2
1 --- 1 --- 3
1 --- 1 --- 4
1 --- 2 --- 0
1 --- 2 --- 1
1 --- 2 --- 2
1 --- 2 --- 3
1 --- 2 --- 4
1 --- 3 --- 0
1 --- 3 --- 1
1 --- 3 --- 2
1 --- 3 --- 3
1 --- 3 --- 4
1 --- 4 --- 0
1 --- 4 --- 1
1 --- 4 --- 2
1 --- 4 --- 3
1 --- 4 --- 4
2 --- 0 --- 0
2 --- 0 --- 1
2 --- 0 --- 2
2 --- 0 --- 3
2 --- 0 --- 4
2 --- 1 --- 0
2 --- 1 --- 1
2 --- 1 --- 2
2 --- 1 --- 3
2 --- 1 --- 4
2 --- 2 --- 0
2 --- 2 --- 1
2 --- 2 --- 2
2 --- 2 --- 3
2 --- 2 --- 4
2 --- 3 --- 0
2 --- 3 --- 1
2 --- 3 --- 2
2 --- 3 --- 3
2 --- 3 --- 4
2 --- 4 --- 0
2 --- 4 --- 1
2 --- 4 --- 2
2 --- 4 --- 3
2 --- 4 --- 4
3 --- 0 --- 0
3 --- 0 --- 1
3 --- 0 --- 2
3 --- 0 --- 3
3 --- 0 --- 4
3 --- 1 --- 0
3 --- 1 --- 1
3 --- 1 --- 2
3 --- 1 --- 3
3 --- 1 --- 4
3 --- 2 --- 0
3 --- 2 --- 1
3 --- 2 --- 2
3 --- 2 --- 3
3 --- 2 --- 4
3 --- 3 --- 0
3 --- 3 --- 1
3 --- 3 --- 2
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