1.將類似如下程序中的切片變得更可讀

            
              ###位置## 0123456789012345678901234567890123456789012345678901234567890'
record = '....................100          .......513.25   ..........'
cost = int(record[20:32]) * float(record[40:48])
            
          

?利用slice()函數(shù)創(chuàng)建slice對(duì)象，該對(duì)象可用于任何切片可應(yīng)用的地方如：

            
              >>> items = [0, 1, 2, 3, 4, 5, 6]
>>> a = slice(2, 4)
>>> items[2:4]
[2, 3]
>>> items[a]
[2, 3]
>>> items[a] = [10,11]
>>> items
[0, 1, 10, 11, 4, 5, 6]
>>> del items[a]
>>> items
[0, 1, 4, 5, 6]
            
          

slice對(duì)象還有很多有趣的方法：

            
              >>> a = slice(5, 50, 2)
>>> a.start
5
>>> a.stop
50
>>> a.step
2
            
          

?a.indices(len)可按給定長度上限生成對(duì)應(yīng)元組

            
              >>> s = 'HelloWorld'
>>> a.indices(len(s))
(5, 10, 2)
>>> for i in range(*a.indices(len(s))):
... print(s[i])
...
W
r
d
            
          

?