007 列表的遍历

for

列表

一维

>>> a = [1, 2, 3, 4, 5]
>>> for i in a:
    print(i)

    
1
2
3
4
5
>>> 

二维

>>> a = [[1, "one"], [2, "two"], [3, "three"]]
>>> for i, j in a:
    print(i, j)

    
1 one
2 two
3 three
>>> 

三维

>>> a = [[[1], ["one"], ["一"]], [[2], ["two"], ["二"]]]
>>> for i, j, k in a:
    print(i, j, k)

    
[1] ['one'] ['一']
[2] ['two'] ['二']
>>> 
>>> b = [[[1, 2], ["one", "two"], ["一", "二"]], [[3, 4], ["three", "four"], ["三", "四"]]]
>>> for i, j, k in b:
    print(i, j, k)

    
[1, 2] ['one', 'two'] ['一', '二']
[3, 4] ['three', 'four'] ['三', '四']
>>> 

for-else

跳过 else

for i in range(5):
    print(i)
    if i == 3:
        break
else:
    print("not break")

>>>

0
1
2
3

执行 else

for i in range(5):
    print(i)
    if i == 8:
        break
else:
    print("not break")

>>>

0
1
2
3
4
not break

while

num = 1
while num < 100:
    print(num)
    num *= 2

>>>

1
2
4
8
16
32
64

while-else

• 用起来跟 for-else 类似
• 跳出循环就不走 else
• 循环正常走完才走 else

break, continue, pass

• break: 结束本层循环
• continue: 结束本次循环，继续本层的新一轮循环
• pass: 当作空语句即可

比较

• for 代码与 while 代码可以互改
• for 的频率高一点
• 一般，明确次数用 for，次数不明用 while