迭代器内的变量是怎么保存的？

有下面一段代码，分别打印 1 1 2 3 5 和 0 0 0 0 0，请问后面一个迭代器为什么不会打印 0 1 2 3 4 ？

class Fib(object):
    def __init__(self):
        self.prev = 0
        self.curr = 1
    def next(self):
        value = self.curr
        self.curr += self.prev
        self.prev = value
        return value
    def __iter__(self):
        return self

class T(object):
    def __iter__(self):
        return self
    def next(self):
        for i in range(5):
            return i

f = Fib()
t = T()

print next(f)
print next(f)
print next(f)
print next(f)
print next(f)

print next(t)
print next(t)
print next(t)
print next(t)
print next(t)