python高级特性-迭代

 概述

for  v   in d.values():

for k,v  in d.items():

for  a    in 'adfa':

#判断对象是否可迭代

from collections import Iterable

isinstance('abc',Iterable)

#添加下标

for x,y in enumerate([(1,1),(2,3),(4,5)]):

详解

1.迭代list

>>> d={'a':1,'b':2,'c':3}

#输出values

 >>> for v in d.values():
 ... print v
 ...
 1
 3
 2

  #同时输出key，value

>>> for k, v in d.items():
...      print k,v
... 
#输出
a 1
c 3
b 2

2.字符串迭代

>>> for a in 'adfa':
...      print a
... 
a
d
f
a

3.判断一个对象是否可迭代

>>>from collections import Iterable
#判断字符串是否可迭代
>>>isinstance('abc',Iterable)
#输出
True
#判断list是否可迭代

>>>isinstance([1,2,3],Iterable)
#输出
True
#判断整数是否可迭代

  >>> isinstance(12345,Iterable)
  False

4.对list实现下标循环

>>> for i,value in enumerate(['a','b','c']):
...      print(i,value)
... 
(0, 'a')
(1, 'b')
(2, 'c')
>>> for i,value in enumerate(['a','b','c']):
...      print  i,value
... 
0 a
1 b
2 c

>>> for x,y in [(1,1),(2,3),(4,5)]:
...      print x,y
... 
1 1
2 3
4 5

>>> for x,y in enumerate([(1,1),(2,3),(4,5)]):
... print x,y
...
0 (1, 1)
1 (2, 3)
2 (4, 5)