class SavingsAccount(object):
    def __init__(self, name, pin, balance = 0.0):
        self._name = name
        self._pin = pin
        self._balance = balance
        
    def __lt__(self,other):
        print("this is <")
        return self._name < other._name

s1 = SavingsAccount("Ken","1000",0)
s2 = SavingsAccount("Bill", "1001",30)  

s1<s2
this is <
False

s1>s2
this is <
True

当s1<s2时调用__lt__方法没有问题，问题是当调用>时貌似也调用了__lt__，但是结果貌似取了一个非操作。这是python 的什么特性？什么情况下会出现这种结果