class Fib(object):

    L = [0,1]

    def __init__(self, num):

        for n in range(num - 2):

            L.append(L[n]+L[n+1])

        self.numbers = L

    def __str__(self):

        return str(self.numbers)

    def __len__(self):

        return len(self.numbers)

f = Fib(10)

print (f)

print (len(f))

会报错  global name 'L' is not defined

class Fib(object):

    def __init__(self, num):

        L = [0,1]

        for n in range(num - 2):

            L.append(L[n]+L[n+1])

        self.numbers = L

    def __str__(self):

        return str(self.numbers)

    def __len__(self):

        return len(self.numbers)

f = Fib(10)

print (f)

print (len(f))

这样为啥就可以