为什么下面正确代码运行出现这种错误？请大家为我解答，谢谢！！！
class Student(object):
def __init__(self, name, score):
self.name = name
self.score = score
def __str__(self):
return '(%s: %s)' % (self.name, self.score)
__repr__ = __str__
def __cmp__(self, s):
if False == isinstance(s, Student):
return -1
return -cmp(self.score, s.score) or cmp(self.name, s.name)
L = [Student('Tim', 99), Student('Bob', 88), Student('Alice', 99)]
print (sorted(L))错误类型：TypeError: '<' not supported between instances of 'Student' and 'Student'
