_cmp_(self,other) 包含了两个对象相比较的所有情况
_eq_(self,other) 判断两个对象相等
_lt_(self,other) 小于
_gt_(self,other) 大于
2.数字运算
_add_(self,other) 加
_sub_(self,other) 减
_mul_(self,other) 乘
_div_(self,other) 除
3.逻辑运算
_or_(self,other) 或者
_and_(self,other) 并且
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