迭代器就是重复地做一些事情，可以简单的理解为循环，在python中实现了__iter__方法的对象是可迭代的，实现了next()方法的对象是迭代器，这样说起来有

    迭代器就是重复地做一些事情，可以简单的理解为循环，在python中实现了__iter__方法的对象是可迭代的，实现了next()方法的对象是迭代器，这样说起来有点拗口，实际上要想让一个迭代器工作，至少要实现__iter__方法和next方法。很多时候使用迭代器完成的工作使用列表也可以完成，但是如果有很多值列表就会占用太多的内存，而且使用迭代器也让我们的程序更加通用、优雅、pythonic。下边是一个例子，从里边你会感受到不用列表而用迭代器的原因。

#!/usr/bin/env python
#coding=utf-8
class Fib:
    def __init__(self):
        self.a,self.b = 0,1
    def next(self):
        self.a,self.b = self.b,self.a+self.b
        return self.a
    def __iter__(self):
        return self
fibs = Fib()
for f in fibs:
    if f < 10000:
        print f
    else:
        break

    迭代器是一个对象，而生成器是一个函数，迭代器和生成器是python中两个非常强大的特性，编写程序时你可以不使用生成器达到同样的效果，但是生成器让你的程序更加pythonic。创建生成器非常简单，只要在函数中加入yield语句即可。函数中每次使用yield产生一个值，函数就返回该值，然后停止执行，等待被激活，被激活后继续在原来的位置执行。下边的例子实现了同样的功能：

 

#!/usr/bin/env python
#coding=utf-8
def fib():
    a,b = 0,1
    while 1:
        a,b = b,a+b
        yield a
for f in fib():
    if f < 10000:
        print f
    else:
        break
生成器接收参数实例：
def counter(start_at):
    count = start_at
    while True:
        print 'before count %s' % count
        val = (yield count)
        print 'after count %s, val %s' % (count, val)
        if val is not None:
            count = val
            print 'sts a'
        else:
            count += 1
            print 'sts b'
           
if __name__ == '__main__':
    count = counter(5)
    print 'calling1 count.next():', count.next()
    print 'calling2 count.next():', count.next()
    print 'calling3 count.next():', count.next()
    print 'calling4 count.next():', count.next()
    print 'calling5 count.next():', count.next()
    print '-------start---------'
    s = count.send(20)
    print 's', s
    print 'calling count.next():', count.next()
    print 'calling count.close():', count.close()
    print 'calling count.next():', count.next()

结果：
calling1 count.next(): before count 5
5
calling2 count.next(): after count 5, val None
sts b
before count 6
6
calling3 count.next(): after count 6, val None
sts b
before count 7
7
calling4 count.next(): after count 7, val None
sts b
before count 8
8
calling5 count.next(): after count 8, val None
sts b
before count 9
9
-------start---------
after count 9, val 20
sts a
before count 20
s 20
calling count.next(): after count 20, val None
sts b
before count 21
21
calling count.close(): None
calling count.next():
Traceback (most recent call last):
  File "D:\Python27\counter.py", line 26, in <module>
    print 'calling count.next():', count.next()
StopIteration

来自为知笔记(Wiz)