Python cookbook(数据结构与算法)对切片命名清除索引的方法

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record='....................100.......513.25..........'
cost=int(record[20:23])*float(record[30:36])

SHARES=slice(20,23) #对切片命名
PRICE=slice(30,36) #对切片命名
cost=int(record[SHARES])*float(record[PRICE])

> items=[0,1,2,3,4,5,6]
> a=slice(2,4)
> a
slice(2, 4, None)
> items[a]
[2, 3]
> items[2:4]
[2, 3]
> items[a]=[77,88]
> items
[0, 1, 77, 88, 4, 5, 6]
> del items[a]
> items
[0, 1, 4, 5, 6]
> 

> items=[0,1,2,3,4,5,6]
> a=slice(2,4)
> a
slice(2, 4, None)
> a.start
2
> a.stop
4
> a.step
> b=slice(1,5,2)
> b
slice(1, 5, 2)
> b.start
1
> b.stop
5
> b.step
2
> 

> items=[0,1,2,3,4,5,6]
> a=slice(2,4)
> a
slice(2, 4, None)
> a.start
2
> a.stop
4
> a.step
> b=slice(1,5,2)
> b
slice(1, 5, 2)
> b.start
1
> b.stop
5
> b.step
2
> s='HelloWorld'
> a.indices(len(s))
(2, 4, 1)
> b.indices(len(s))
(1, 5, 2)
> items[a]
[2, 3]
> items[b]
[1, 3]
> for i in range(*a.indices(len(s))):
  print(s[i])
l
l
> for i in range(*b.indices(len(s))):
  print(s[i])
e
l
> c=slice(0,8,2)
> c
slice(0, 8, 2)
> for i in range(*c.indices(len(s))):
  print(s[i])
H
l
o
o
>