退出双层循环： 方式1：try--except
代码语言：javascript复制try:
for i in range(5):
for j in range(5):
if i==3 and j ==3:
raise
except:
print(1)
pass方式2：函数实现的return
代码语言：javascript复制def fun():
for i in range(5):
for j in range(5):
print(i,j)
if i==3 and j ==3:
return True
fun()方式3：多层break
代码语言：javascript复制for i in range(5):
for j in range(5):
for k in range(5):
if i == j == k == 3:
break
else:
print (i, '----', j, '----', k)
else: continue
break
else: continue
break习题12：输入3个数字，达到3个数字求和，结束程序
代码语言：javascript复制result = 0
for i in range(3):
number = input("please input number: ")
result = int(number)
print(result)
习题13、 用户输入不同的数据，当输入的数据达到3个数字的时候，求和结束程序。（数字可以是整数）
提示：判断是否整数的方法，isdigit()
遍历所有的输入数据，判断是否在0-9的字符串范围内
方式1：
#coding=utf-8
result = 0
count = 0
while True:
s = input("please input the number: ")
for v in s:
if v not in "0123456789":#如果不是数字跳出当前循环
break
else:
count =1
result = int(s)
if count ==3:
break
print(result)方式2：先定义一个判断数字的函数
代码语言：javascript复制#encoding=utf-8
def is_int(num):
for n in num:
if n not in "0123456789":
return False
return True
result = 0
number_count = 0
while True:
s = input("please input the number: ")
if is_int(s):
result = int(s)
number_count = 1
if number_count == 3:
break
print(result)方式3：利用isdigit()函数
代码语言：javascript复制result1 = 0
count1=0
while True:
s = input("please input the number: ")
if s.isdigit():
count1 =1
result1 = int(s)
if count1 ==3:
break
print(result1)习题14：用嵌套列表的方式，遍历输出一个矩阵 方式1：
代码语言：javascript复制l = [
[1,2,3],
[4,5,6],
[7,8,9]
]
for i in l:
for j in i:
print(j,end=" ")
print()方式2：
代码语言：javascript复制for i in range(len(l)):
for j in range(len(l[i])):
print(l[i][j],end = " ")
print()习题15：嵌套列表的正、反对角线之和 正对角线之和
代码语言：javascript复制l = [
[1,2,3],
[4,5,6],
[7,8,9]
]
rusult = 0
for i in range(len(l)):
for j in range(len(l[i])):
if i==j:
rusult = l[i][j]
print(rusult)反对角线之和
代码语言：javascript复制rusult = 0
for i in range(len(l)):
for j in range(len(l[i])):
if (i j)==2:
rusult = l[i][j]
print(rusult)习题16：求以下矩阵四边元素之和 l = [ [1,2,3,4,5], [1,2,3,4,5], [1,2,3,4,5], [1,2,3,4,5], [1,2,3,4,5] ]
方法1：
1、第1行和第5行所有元素求和 2、其他行 只要第1列和第5列求和
代码语言：javascript复制rusult = 0
for i in range(len(l)):
for j in range(len(l[i])):
if i == 0 or i == 4:
rusult = l[i][j]
else:
if j==0 or j==4:
rusult = l[i][j]
print(rusult)方法2：所有元素之和，减去中间矩阵之和
代码语言：javascript复制l = [
[1,2,3,4,5],
[1,2,3,4,5],
[1,2,3,4,5],
[1,2,3,4,5],
[1,2,3,4,5]
]
matrix_element_sum = 0
sub_matrix_element_sum = 0
for i in range(len(l)):
for j in range(len(l[i])):
matrix_element_sum = l[i][j]
result_mid = 0
for i in range(len(l)):
for j in range(len(l[i])):
if i == 0 or i ==4:
continue
else:
if j !=0 and j!=4:
sub_matrix_element_sum = l[i][j]
print(matrix_element_sum - sub_matrix_element_sum)
