Python翻转字符串或者列表的方式

1. reversed

class reversed(object)
 |  reversed(sequence) -> reverse iterator over values of the sequence
 |  
 |  Return a reverse iterator
 |  
 |  Methods defined here:
 |  
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name
 |  
 |  __iter__(...)
 |      x.__iter__() <==> iter(x)
 |  
 |  __length_hint__(...)
 |      Private method returning an estimate of len(list(it)).
 |  
 |  next(...)
 |      x.next() -> the next value, or raise StopIteration
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __new__ = <built-in method __new__ of type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

处理的对象是可迭代对象，返回值是一个迭代器，所以可以处理string list 等，如下：

In [54]: reversed([1,2,3])                                                                                                                                                                        
Out[54]: <listreverseiterator at 0x7f835810c190>

In [55]: reversed('123')                                                                                                                                                                          
Out[55]: <reversed at 0x7f835810c2d0>

In [56]: type(reversed('123'))
Out[56]: reversed

In [57]: for i in reversed('123'):
   ....:     print i
   ....:     
3
2
1

PS： list内置__reversed__()方法实现的功能和此类似，使用方法见2

2. reverse

reverse是list内置的一个方法，所以只能对list使用，如下：

In [62]: l = [1, 2, 3]                                                                                                                                                                            

In [63]: l.reverse()

In [64]: l
Out[64]: [3, 2, 1]

__reversed__()

In [65]: l.__reversed__()
Out[65]: <listreverseiterator at 0x7f835810ca90>

In [66]: for i in l.__reversed__():                                                                                                                                                               
   ....:     print i
   ....:     
1
2
3

3. 切片

最简单的一种方法了，可以对string和list使用

In [73]: s
Out[73]: 'i am a student.'

In [74]: s[::-1]
Out[74]: '.tneduts a ma i'

In [75]: l
Out[75]: [3, 2, 1]

In [76]: l[::-1]
Out[76]: [1, 2, 3]