self.numbers = L

print 'self.numbers is list?',isinstance(self.numbers,list)

print len(L)

def __str__(self):

    t = str(self.numbers)

    print 'self.numbers now is str?',isinstance(t,str)

    print len(t)

    return t

__repr__ = __str__

def __len__(self):

    return len(self.numbers)

结果：

self.numbers is list? True

10

self.numbers now is str? True

33

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

10