class Fib(object):

    def __init__(self, num):
        a = 0
        b = 1
        l = []
        for n in range(num):
            l.append(a)
            a,b = b,a+b #这一段有问题
        self.numbers = l  
   
    def __str__(self):
        return str(self.numbers)
       
    __repr__ = __str__
   
  
    def __len__(self):
        return len(self.numbers)

f = Fib(10)
print (f)
print (len(f))

如果我用a,b = b,a+b就输出正常，但是我用

a = b

b = a+b

输出就不对