python進階特性-疊代

 概述

for  v   in d.values():

for k,v  in d.items():

for  a    in 'adfa':

#判斷對象是否可疊代

from collections import Iterable

isinstance('abc',Iterable)

#添加下标

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

詳解

1.疊代list

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

#輸出values      

 >>> for v in d.values():

 ... print v

 ...

 1

 3

 2

  #同時輸出key，value

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

2.字元串疊代

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

3.判斷一個對象是否可疊代

>>>from collections import Iterable
#判斷字元串是否可疊代
>>>isinstance('abc',Iterable)
#輸出
True
#判斷list是否可疊代      

>>>isinstance([1,2,3],Iterable)
#輸出
True
#判斷整數是否可疊代      

  >>> isinstance(12345,Iterable)

  False

4.對list實作下标循環

>>> 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)