Visualizing the Hierarchy

1. sort instance through __lt__

#sort people,return True if self's name is lexicographically
less than other's name, and False otherwise
def __lt__(self, other):
    if self.lastName == other.lastName:
        return self.name < other.name
    return self.lastName < other.lastName


# sorting MIT people uses their ID number, not name!
def __lt__(self, other):
    return self.idNum < other.idNum

2.不同层级的class之间的比较

p1 = MITPerson(‘Eric’)

p2 = MITPerson(‘John’)

p3 = MITPerson(‘John’)

p4 = Person(‘John’)

现象：

p1 < p4 Attribute Error

p4 < p1 False

原因：