迭代器

##迭代器
In [24]: ci = collections.Co
collections.Container collections.Counter

In [24]: ci = collections.Counter('1112312312sdfsdf')

In [25]: ci
Out[25]: Counter({'1': 5, '2': 3, 'd': 2, 'f': 2, 's': 2, '3': 2})

In [26]: ci.elements()
Out[26]: <itertools.chain at 0x7f8fd4f1b590>

In [27]: c2 = ci.elements()

In [28]: c2.next()
Out[28]: 'd'
##类里必须有__iter__

内部实现：内部实现有没有下一个

##生成器

基于yield生成

In [54]: range(10)
Out[54]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

In [55]: xrange(10)
Out[55]: xrange(10)
应用：
In [58]: listOne = [1,2,31,4,32]

In [59]: for i in range(len(list))
list listOne

In [59]: for i in range(len(listOne)):
....: print lis
list listOne
....: print listOne[i]
....:
1
2
31
4
32