python yield 用法

yield.py

class Fib:
    def __init__(self, max):
        self.max = max
    
    def __iter__(self):
        self.a = 0
        self.b = 1
        return self
    
    def next(self):
        fib  = self.a
        if fib > self.max:
            raise StopIteration
        self.a, self.b = self.b, self.a + self.b
        return fib
        
for n in Fib(100):
    print n