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
>>>