生成器：只有在调用的时候才会生成相应的数据
只能逐个往后取（不能取前面的，也不能直接跳到后面）
只有一个__next()__方法（Python3）next()（Python2）
两种实现方式
1.生成器表达式，语法看似列表推导式，只是把最外层的中括号改为小括号。
>>> a = (i for i in range(8)) >>> a <generator object <genexpr> at 0x000001D1C9FB8A98> >>> dir(a) [‘__class__‘, ‘__del__‘, ‘__delattr__‘, ‘__dir__‘, ‘__doc__‘, ‘__eq__‘, ‘__format__‘, ‘__ge__‘, ‘__getattribute__‘, ‘__gt__‘, ‘__hash__‘, ‘__init__‘, ‘__iter__‘, ‘__le__‘, ‘__lt__‘, ‘__name__‘, ‘__ne__‘, ‘__new__‘, ‘__next__‘, ‘__qualname__‘, ‘__reduce__‘, ‘__reduce_ex__‘, ‘__repr__‘, ‘__setattr__‘, ‘__sizeof__‘, ‘__str__‘, ‘__subclasshook__‘, ‘close‘, ‘gi_code‘, ‘gi_frame‘, ‘gi_running‘, ‘gi_yieldfrom‘, ‘send‘, ‘throw‘]
2.函数（通过yield关键字）
#coding=utf-8 def natural_number(): ‘‘‘自然数‘‘‘ n = 0 while True: yield n n += 1 n = natural_number() print n.next() print n.next() print n.next() print n.next() print n.next() 0 1 2 3 4
#coding=utf-8 def fib(x): # 斐波拉契数列 n, a, b = 0, 0, 1 while n < x: yield b a, b = b, a + b n += 1 f = fib(6) print f.next() print f.next() print f.next() print f.next() print f.next() print f.next() 1 1 2 3 5
迭代器
原文：https://www.cnblogs.com/allenzhang-920/p/8922662.html