【Python练习cookbook】切片slice高级应用

1.将类似如下程序中的切片变得更可读

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

 利用slice()函数创建slice对象，该对象可用于任何切片可应用的地方如：

>>> 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对象还有很多有趣的方法：

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

 a.indices(len)可按给定长度上限生成对应元组

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