2018-10-23 Python34 迭代器Iterator、

判断一个对象是否可迭代：

In [6]: from collections import Iterable

In [7]: isinstance([], Iterable)
Out[7]: True

In [8]: isinstance({}, Iterable)
Out[8]: True

In [9]: isinstance("", Iterable)
Out[9]: True

In [10]: isinstance(100, Iterable)
Out[10]: False

迭代器

可以用next()获取下一个值

In [20]: x = (i for i in range(10))

In [21]: next(x)
Out[21]: 0

In [22]: next(x)
Out[22]: 1

In [23]: next(x)
Out[23]: 2

In [24]: next(x)
Out[24]: 3

In [27]: isinstance(x, Iterator)
Out[27]: True

iter() 函数

可以将可迭代对象，变成迭代器：

In [30]: a = [11,22,33]

In [31]: isinstance(a, Iterator)
Out[31]: False

In [32]: iter(a)
Out[32]: <list_iterator at 0x7f0dee3abc50>

In [33]: b = iter(a)

In [34]: isinstance(b, Iterator)
Out[34]: True

In [35]: next(b)
Out[35]: 11

In [36]: next(b)
Out[36]: 22

In [37]: next(b)
Out[37]: 33

包含yield的函数，是生成器

不会结束程序的return，是迭代器，能用next()取下一个值。

In [57]: type(x for x in range(10))
Out[57]: generator


In [59]: def gen(max):
   ....:     n = 0
   ....:     while n<max:
   ....:         yield n
   ....:         n+=1
   ....:         
In [60]: type(gen)
Out[60]: function
In [61]: type(gen(10))
Out[61]: generator
In [63]: for i in gen(10):
   ....:     print(i)
   ....:     
0
1
2
3
4
5
6
7
8
9

相当于：

from collections import Iterator

class Gen(object):
    def __init__(self,max):
        self.max=max
        self.n=0

    def __iter__(self):
        return self

    def __next__(self):
        if self.n<self.max:
            tmp=self.n
            self.n+=1
            return tmp
        raise StopIteration


print(isinstance(Gen(10), Iterator) )
for i in Gen(10):
    print(i, end=' ')

True
0 1 2 3 4 5 6 7 8 9