Python for循环与getitem的关系详解

In [169]: class Foo:
   ...:   def __getitem__(self, pos):
   ...:     print(pos)
   ...:     return range(10)[pos]
   ...:  

In [172]: for i in f:
   ...:   ...
   ...:   
   ...:                                             
0
1
2
3
4
5
6
7
8
9
10

In [173]: class Foo:
   ...:   def __getitem__(self, pos):
   ...:     if pos >5:
   ...:       raise StopIteration
   ...:     print(pos)
   ...:     return range(10)[pos]
   ...: 

In [177]: for i in f:
   ...:   ...
   ...:                                             
0
1
2
3
4
5

   ...:   def __getitem__(self, pos):
   ...:     if pos >5:
   ...:       raise IndexError
   ...:     print(pos)
   ...:     return range(10)[pos]
   ...:                                             
 
In [182]:                                             
 
In [182]: f = Foo()                                        
 
In [183]: for i in f:
   ...:   ...
   ...:                                             
0
1
2
3
4
5

In [184]: list(f)                                         
0
1
2
3
4
5
Out[184]: [0, 1, 2, 3, 4, 5]

In [185]: from collections import Iterable                            
In [186]: isinstance(f, Iterable)                                 
Out[186]: False
 
In [187]: iter(f)                                         
Out[187]: <iterator at 0x114f2be50>

dir(f)                                         
Out[189]:
['__class__',
 '__delattr__',
 '__dict__',
 '__dir__',
 '__doc__',
 '__eq__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getitem__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__le__',
 '__lt__',
 '__module__',
 '__ne__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__']